Imagens das páginas
PDF
ePub

unlike a footprint in sand. P. Agamemnon exhibits a singular variety: the footstalk is to one side of a filiform scale, scarcely distinguishable, except under a high power, from hairs. These are toothed at their upper extremity. Another scale, almost peculiar to the species, is diamond-shaped. It bears a close resemblance to the ace of diamonds. The scales on the under wing of Parnassus Apollo are for the most part leaf-shaped, but more obtuse than those of Papilio Polydamus; whilst certain scales of Parnassus Phabus very nearly resemble those of P. Apollo. They occupy different positions,—a diversity between two closely-allied species worth noting, and of service in the determination of specific identity.

From the pretty little genus Thais, one of the Mediterranean fauna, is obtained an elegant scale, in form resembling a single flower of the Lily of the Valley, and may, in future, be distinguished as the "Lily-scale.' F. Cassandra furnishes, besides the "Lily-scale," another of an irregular shape, threepointed, elongate, and not unlike an ancient partisan or halberd. Anthocaris Eupompi (Orange-tip), of Sierra Leone, furnishes us with a white scale, irregular in form, and with a double footstalk: its orange scales have triple footstalks, and are remarkably attractive objects under a medium power. Seen in clusters on the wing, they form a brilliant prismatic band of a golden hue. The scales of Pieris Daplidice, although leaf-shaped, are widely cleft; while those of P. Belia afford typical examples of the "battledore scale." The scales of P. Pyrrha differ in the two sexes, and are diversified in form and other characters. Triangular scales, confined to the anterior portion of the wings, are found in all the Callidryas, and among the genus Colias the lily-shaped scale prevails. A somewhat remarkable scale is found on the wing of the female Colias Edusa (it is something like a phial-bottle), and in an Indian species an arrowheaded scale. A wing scale of Idea Hestia bears a striking resemblance to a fragment of sea-weed (Fucus). It is triangular in form, and deeply serrated, while scales taken from other portions of the wing are very nearly square. Among the beautiful species Argynnidæ, a very few scales presenting variety are found. One bears a resemblance to a palm-branch, and for this reason may be designated the "palmbranch scale."

From these cursory observations it will be seen that the scales of Lepidoptera present attractive variations, which furnish evidence of that beauty of design that generally pervades the works of Nature.

[blocks in formation]

OUR COMMON BRITISH FOSSILS, AND WHERE TO FIND THEM.

MY

No. IV.

BY J. E. TAYLOR, F.G.S., &c.

Y readers will have seen from the illustrations accompanying the last article on this subject, the strong external resemblances between the earliest King-crabs, such as the Belinurus, and one genus of Silurian Trilobites (Trinucleus). The chief apparent difference is in the ends of their bodies, that of the King-crab being prolonged into the dart shape which gives to it its generic name, whilst in the Trinucleus It is round. But we have only to glance at figures of various kinds of Trilobites to see that they vary among themselves in this respect. Thus in Asaphus caudatus (fig. 13), one of the commonest of Lower Silurian Trilobites, we have the pygidium, or tail, drawn out into a point.

Fig. 48. Paradoxides Davidis.

Undoubtedly the Trinucleus (fig. 17) is one of the prettiest of Trilobites. It has a look which suggests the mysterious Egyptian figures of ancient courtiers! The head or cephalic shield is much developed, and on each side is prolonged into two spines half as long again as the body. Like the Agnostus and several others, the Trinucleus had no eyes. In this respect we find the various genera of Trilobites differing very much from each other. Some have a very large number, as Asaphus tyrannus; and thence we find them decreasing until they are absent altogether. All the genera of the order Trinucleida, however, are not eyeless; and this illustrates the uncertainty with

[merged small][merged small][graphic]
[graphic]

cephalic shield, is usually found alone; the thorax, or ringed part, is also abundantly found separate; whilst the pygidium, or tail, is frequently met with apart

the female has none; but this is entirely due to the very different habits of life of the two sexes. Trinucleus is abundant in the Caradoc shales of Shropshire.

From the Cambrian to the Carboniferous formations we find certain Trilobites peculiar to the various geological systems. Thus, Paradoxides and Agnostus are peculiarly Cambrian; Trinucleus and Asaphus are almost exclusively Lower Silurian; Phacops and Calymene are markedly Upper Silurian; Brontes and Harpes are among characteristic Devonian fossils; whilst Phillipsia and Griffithsides are genera of small Trilobites-the last of their race-which are peculiar to the Carboniferous limestones.

Fig. 53. Ogygia Buchii.

from the others, although it is usually adhering to the thoracic part. Of course, animals which have died and been buried in the mud are found with all the above parts adhering to each other. The carapace or shell differed in its character in various species. In

some it appears to have been very thin, in others harder. As a rule, it was chitinous, after the manner of the elytra of beetles, although there can be no doubt this was often strengthened by the presence of limy matter. In the carboniferous Trilobites (Phillipsia, &c.) the carapace seems to have contained more limy matter in its composition than other species. In this genus we always find the moultings in the two parts of body and tail, and head. In the Calymenes (fig. 14) the thoracic or ringed part is frequently found by itself, and not seldom the rings are detached, as if the whole mechanism of the coatof-mail-like armour had become loosened and got scattered about. Undoubtedly the chemical composition of the carapace differed accordingly as the habits of the Trilobites varied.

The Cambrian Trilobites, as a rule, differ from their

[merged small][graphic][subsumed]

D

Fig. 55. Trinucleus Lloydii.

[merged small][merged small][merged small][graphic]

Fig. 54. Head-shield and Caudal shield of Phillipsia.

Silurian descendants and representatives in having a larger number of rings or segments to the thoracic (or middle) part of the body. The tail part (caudal shield) is, however, less developed than in the Silurian species. The side-lobes of some genera, Paradoxides and Acidaspis, are fringed, and, in the case of the latter, further adorned with spines. Some of these may have been sexual distinctions, although we are now forced to regard them as specific. Dean Buckland and many other naturalists have regarded an isopod crustacean abundant in the seas around Tierra del Fuego and the Straits of Magellan, as being nearly allied to this group of Trilobites. This crustacean is called Serolis. Its cephalic shield has compound sessile eyes, arranged in halfmoon-shaped lobes exactly like those of some Trilobites. The segments or joints of the thoracic portion of the body are fringed, as in Paradoxides, and there is a movable caudal or tail shield, as in Phacops caudatus, an abundant Silurian Trilobite. Only the antennæ and mouth-organs differentiate them. But these are very thin and weak, and after death may soon be detached, as various geologists believe was the case with some Trilobites. The legs are fitted for crawling about, but, as is frequent in animals living in sea-water, they are also weak and thin. The Serolis is a slow crawler and swimmer, and is usually found on sea. weed. Some geologists have imagined that a few

Fig. 58. Apus productus.

The Cambrian strata have recently been made to extend upwards as high as the "May Hill" group, so as to include rocks formerly classed as Lower Silurian. They are well represented in many parts of Great Britain, notably in North Wales and the Lake districts. Trilobites of various genera may be met with in many localities which are usually visited by tourists for the sake of the scenery alone. It is one of the privileges of the geologist, that his calling takes him to some of the wildest, grandest, or most beau

tiful scenes in nature. Although, in not a few instances, rich fossiliferous strata occur in unlovely places, amid densely-populated neighbourhoods, as at the Wren's Nest, near Dudley; yet as a rule fossils are most abundant where the rocks crop out along mountain or hill sides or sea-cliffs. In searching for them he startles the grouse or the moor-fowl, finds many a lovely mountain plant solitarily blooming, and inhales fresh air which seems to him like draughts of old wine! Scenes of unsurpassed loveliness are thus revealed to him, in the grandeur of rock-masses, or the panoramic stretch of the valleys below and beyond. What wonder if men who have had to toil the year round for the bread which perisheth, in dingy offices or amid the noise and bustle of machinery, should so value the week or two of summer holiday, which enables them to devote themselves to those geological pursuits which have all the charm and excitement of hunting without any of its cruelty! For, if the geologist wish to change the area of his labours from the mountainside to the sea-side, he can do so at leisure, without interfering with his success in fossil-hunting. Some of the very best sections are those to be seen in our sea-cliffs-some of the richest fossiliferous districts are where the student may be taking in a fresh stock of health whilst he is following his bent, and have silently impressed on his memory scenes of beauty which will last as long as his own individuality! Perhaps it is this direct contact with Nature in all her varied moods which makes such enthusiasts of geologists. Not even botanists are more devoted to their hobby; and it is undoubtedly this enthusiasm which makes geological investigation not to depend upon companionship for success.

The recent absorption of most, if not all, the Lower Silurian rocks into the Cambrian system has, of course, largely added to the number of localities where fossils are to be obtained. The Menevian beds near St. David's, in South Wales, are exceedingly rich in Trilobites; among which Paradoxides Davidis, the largest of its order, is abundant. This species sometimes attains a length of two feet, and is, therefore, strongly contrastable in this respect with the little Agnostus (fig. 21) and the Phillipsia (fig. 54). The South Welsh valleys are little explored, although the geological student might do so to his double advantage, for they are equally rich in scenery and in fossils. Monmouthshire presents an area of country where we have, perhaps, a more varied geological outcrop than anywhere else in Great Britain. Near Newport a patch of Silurian strata abounds in several species of Trilobites, notably Asaphus and Ogygia (figs. 13 and 53).

Maentrog and Port Madoc have long been celebrated for their rich yields of Trilobites. The student may obtain them, in many places, from the slates which build up the walls by the roadside, whilst in the quarries there are usually bands or seams especially full of them. Few localities are better worth

a visit, for we are here within the charming circle of Snowdonia. The lower Lingula flags are well developed at Maentrog, and one Trilobite is so abundant in them that it was proposed to call them "Olenus" beds. Two species of the obscure little Agnostus are associated with it, along with various other fossils. At no great distance up the higher parts of the valley is Festiniog. A diminutive railway, with cars of the same proportion as the narrow diameter of its "permanent way," runs up one side of the valley to Festiniog, and the geological student can take advantage of it in his rambles, and thus pass over the outcrop of beds rich in Trilobites. Another locality for Cambrian Trilobites is the neighbourhood of Dolgelly, a district whose magnificent scenery of wild mountain and umbrageous valley is annually drawing to it a larger number of tourists and visitors. Here Conocoryphe, Agnostus, &c. may be found in certain places in tolerable abundance. The student might advantageously work his way to Dolgelly by Tremadoc, at which place he will find abundant employment for his hammer. At the village of Penmorfa the slates are often crowded with remains of Trilobites. Garth Hill is also a capital collectingground. In many places the Llandeilo flags are so full of Trilobites that Sir Roderick Murchison gave them the name of "Trilobite Schists." Perhaps the neighbourhood of Builth is the best place for obtaining them. Several species of Ogygia occur, associated with numerous other fossils.

The Cambrian and Silurian rocks of the Lake district are not so abundant in Trilobites as those of North Wales and Shropshire, although we have found them in the rich fossiliferous shales of Applethwaite Common, and on the Lancashire side of Windermere,-chiefly Asaphus. Calymene, Homalonotus, and others occur in the Dafton shales, of Upper Llandeilo age. In the Coniston limestone, also, we have Ilianus, Cheirurus, Agnostus, &c., all of them well-marked genera of Trilobites.

In the Silurian proper (the upper Silurian of geologists only a few years ago), we find Trilobites reaching their maximum of existence, both in genera, species, and individuals; and we have tolerably certain evidence that after this epoch they began to decline until they became extinct. In the loveliest parts of North Wales, as at Conway, the Devil's Bridge (near Pentre Voelas), Craig Hir, and at Mynydd Fronfrys, about four miles from Llangollen, among the mountains, we find abundance of fossils, and among them are various species of Phacops, Calymene, &c. The pretty village of Woolhope, near Hereford, is another charming collecting-ground, rich in Upper Silurian fossils; and here we find Illænus, Homalonotus, Phacops, &c. Trilobites are also abundant in the Wenlock shales forming part of the Malvern Hills. Of the Dudley limestone and its treasury of these peculiar ancient forms of life, we have already spoken. The neighbourhood of Ludlow

has also long been known as a rich storehouse of Trilobites of various species and genera.

In the Devonian beds it is only here and there we can meet with Trilobites in any abundance. One of the best localities we know of is Newton Abbot, in Devonshire, where the limestone contains numerous Trilobites. The Pilton beds yield certain species of Phacops in plenty. The Trilobites are most abundant in the Middle Devonian strata of England, owing to the probable fresh-water conditions under which most of the other beds were deposited. The carboniferous limestone, both of England and Ireland, is frequently rich in Trilobites of the genera Phillipsia and Griffithsides, named after two distinguished geologists. At Castleton, in the Peak of Derbyshire, along the outcrop of the strata forming Tre-cliff, is a band especially crowded with Phillipsia; and in the curious gorge to the immediate south of the cavern called "Cave Dale" (undoubtedly an ancient cavern with the roof worn off), we may find this Trilobite associated with a wonderfully abundant collection of other fossils. At Salt Hill, Clitheroe, in Lancashire, the shales which part the limestone bands are seen crowded with the evidently moulted remains of Phillipsia.

The large number of species, even of British Trilobites, obtained from the various strata above mentioned, are grouped into certain families. We have first the Agnostidæ, characterized by their small size, by the head and tail being covered with two nearly equal shields, and the possession of not more than two body-rings. This family was eyeless. The Olendide or Paradoxide had long bodies, with numerous free segments. The caudal or tail shield was small; the side lobes were prolonged into curved spines. A large number of the more ancient genera of Trilobites belong to this family. The Asaphida were tolerably large oval Trilobites, with smooth carapaces, and possessed about eight body-rings. Illanus and Ogygia are included in this group. The Trinucleide had a large head-shield, ending in two long spines, one on each side. The body-rings were five or six in number. The Cheirurida included seven distinct genera, which had a geological range from the Cambrian to the Devonian strata. facial sutures of the head-shield ended on the outer margin. The number of rings or segments was eleven, and these were free at their ends. The Calymenida had carapaces roughened over with granules or tubercles, and the number of body-rings was usually thirteen. In Homalonotus, one of the two genera composing this family, the body-rings are not so distinctly trilobed as usual. Phacopide was a family of Trilobites with large facetted eyes. The number of body-rings is eleven. The Lichade had small head-shields, and a tail or pygidium with a broad limb. It contains only the genus Lichas. The Proctida includes the carboniferous genera Phillipsia and Griffithsides. Their number of body-rings was

The

usually nine. The carapace of Phillipsia is generally roughened with granules. Acidaspida had a very ornamental carapace, with eight to ten body-rings, and the segments of the side lobes (pleura) directed backwards. The tail had also two or three segments, furnished with prominent spines. The Bronteida had a large expanded tail or pygidium. The Harpeida were noted for the horseshoe-shaped head-shield, whose angles were greatly prolonged. The body was numerously jointed, usually with twenty-six segments. Only one genus, Harpes, belongs to it. Lastly, we have the Cyphaspida, whose head-shield was also prolonged into spines, and the carapace marked by spiny or pitted surface ornamentations. The number of body-rings varied in the different genera from ten to twenty-two. These are among the less common of the Trilobites. It will give us much pleasure to hear from any correspondents respecting habitats where any genus of species of Trilobite is to be plentifully found.

METROPOLITAN NATURAL HISTORY AND MICROSCOPICAL CLUBS.

HE following is a list of some of the clubs in London devoted to natural history pursuits,

&c. :

Medical Microscopical Society (founded December, 1872).—This society meets at the Century Club, 6, Pall-mall-place, W., on the third Friday of each month from October to May inclusive, at 8 p.m. There is no entrance-fee, and the subscription is IOS. per annum.

The members are qualified members of the medical profession and students of medicine or comparative histology whose qualifications are acceptable to the society. The objects of the society are the discussion of questions in normal and pathological histology, medico-legal and medico-chemical microscopy, mechanical and optical arrangements requisite for the proper examination of specimens, the preparation of the same, &c.; the formation of a cabinet of preparations for the use of members, and the exchange of specimens and material. The officers for 1877 are-President, H. Power, F.R.C.S., &c.; Hon. Secretaries, J. W. Groves, C. H. Golding-Bird.

South London Entomological Society (established 1872).-Meets at the Assembly-rooms, 104, Westminster-bridge-road, S.W. (side entrance). Presi dent, 1877, Mr. J. Platt Barrett, Radnor-street, Peckham. The society has been formed to promote entomological science in South London. Meetings of the members are held every alternate Thursday, from 8 to 10 p.m., in the above Assembly-rooms, when papers are read, exhibitions of specimens made, and discussions take place. A library is being formed as rapidly as funds will permit, all surplus money being devoted to the purchase of books. The society's room is easy of access from all parts of

« AnteriorContinuar »