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The periodic time of 274 years is well indicated by these dates,

A.D. 288 to 1439........ ............ 42 periods of 27:405 years each.
1439 to 1743........ ............ II

27.636
1743 to 1798.

..... 2

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“ If these periods are correct, it is a remarkable coincidence that the aphelion distances of the meteoric rings of April 18th-20th, October 15th21st, November 14th, and December 11th-13th, as well as those of the comets 1866 I., and 1867 I. are all nearly equal to the mean distance of Uranus."

4. Beiträge zur Kenntniss der Sternschnuppen, von Dr. Edmund Weiss (Sitzungsberichte of the Imperial Academy of Vienna for January 16, 1868) presents a short summary of the mathematical problems required to be solved in the determination of the parabolic orbit, and the actual relative speed of the meteors' course in the atmosphere, from the known position of the radiant-point; and shows how approximate calculations of the velocities of shooting-stars have led to discoveries, in proving certain periodical meteorcurrents to be intimately connected with comets of which the orbits have recently been determined *.

5. The Fuel of the Sun, by W. Mattieu Williams, F.C.S. (8vo, 222 pp. Simpkin and Marshall).—An attempt to explain convulsions of the sun's surface by planetary disturbances of a universal atmosphere collected in greatest density about the larger bodies of the solar system, and agitated by tides arising from their several attractions, is the theory for the establishment of which a collection of the greatest interest of recent observations of solar physics has been brought into a small compass by the author of the work, and is well directed to explain the chief phenomena of solar physics. The corona is regarded (Chapter XIII.) as originating in solar projectiles driven from its surface with eruptive violence. In the following chapter the source of meteorites is conjectured to be the solar projectiles which thus pass beyond the boundaries of the zodiacal light; some of which being confined to revolve in two principal orbits outside of that luminary, and in several intermediate zones of irregularly and more thinly scattered projectiles, may be regarded as giving rise to the August and November, as well as to other minor and more or less regular meteoric displays. Somewhat more important speculations and descriptions of the meteorology of the moon and planets, as well as of the distribution of the nebulæ, suggesting the stellar origin of some of those bodies, occupy the greater portion of the remainder of the work.

* The velocity of the April meteors, or Lyraïds, of the 20th of April meteoric shower, relatively to the earth, is given in Dr. Weiss's list of radiant-points and relative velocities of cometary orbits, in the above paper, as 1.585, that of the earth in its orbit being unity. Adopting the value of 18.6 miles per second for the earth's mean orbital velocity, this gives the relative velocity of the Lyraïds, or April shower-meteors, 29.5 miles per second ; very nearly that observed (30 miles per second) in the case of the only shooting-star of the shower doubly observed, as described in this Report, on the night of the 20th of April last.

Fifth Report of the Committee, consisting of HENRY WOODWARD, F.G.S.,

F.Z.S., Dr. Duncan, F.R.S., and R. ETHERIDGE, F.R.S., on the Structure and Classification of the Fossil Crustacea, drawn up by

Henry WOODWARD, F.G.S., F.Z.S. SINCE I had last the honour to present a Report on the Structure and Classification of the Fossil Crustacea, I have published figures and descriptions of the following species, namely :

DECAPODA BRACHYURA. 1. Rhachiosoma bispinosa, H. Woodw. Lower Eocene, Portsmouth. 2. — echinata, H. W. Lower Eocene, Portsmouth.

3. Palæocorystes glabra, H. W. Lower Eocene, Portsmouth. All figured and described in Quart. Journ. Geol. Soc. vol. xxvii. p. 90, pl. 4.

DECAPODA MACRURA. 4. Scyllaridia Belli, H. W. London Clay, Sheppey. Geol. Mag. 1870, vol. vii. p. 493, pl. 22. fig. 1.

AMPHIPODA. 5. Necrogammarus Salweyi, H. W. Lower Ludlow, Leintwardine. Figured and described Trans. Woolhope Club, 1870, p. 271, pl. 11.

ISOPODA, 6. Palæga Carteri, H. W. Lower Chalk, Dover, &c. Geol. Mag. 1870, vol. vii. p. 493, pl. 22. fig. 1.

7. Præarcturus gigas, H. W. Old Red Sandstone, Rowlestone, Herefordshire. Trans. Woolhope Club, 1870, p. 266.

MEROSTOMATA. 8. Eurypterus Brodiei, H. W. Quart. Journ. Geol. Soc. 1871, August. Trans. Woolhope Club, 1870, p. 276.

• PHYLLOPODA. *9. Dithyrocaris tenuistriatus, MoCoy. Carboniferous Limestone, Settle, Yorkshire.

10. Dithyrocaris Belli, H. W. Devonian, Gaspé, Canada.
11. Ceratiocaris Ludensis, H. W. Lower Ludlow, Leintwardine,

12. Ceratiocaris Oretonensis, H. W. Carboniferous Limestone, Oreton, Worcestershire.

13. Ceratiocaris truncatus, H. W. Carboniferous Limestone, Oreton, Worcestershire.

Figured and described in the Geol. Mag. 1871, vol. viii. p. 104, pl. 3. 14. Cuclus bilobatus, H. W. Carboniferous Limestone, Settle, Yorkshire. 15. - torosus, H. W. Carboniferous Limestone, Little Island, Cork. 16. — Wrightii, H. W. Carboniferous Limestone, Little Island, Cork. 17. - Harknessi, H. W. Carboniferous Limestone, Little Island, Cork. *18. — radialis, Phillips. Carboniferous Limestone, Settle, Yorkshire, Visé, Belgium.

*19. Cyclus Rankini, H, W. Carboniferous Limestone, Carluke, Lanarkshire. [*20. — “Brongniartianus,” De Kon, Carboniferous Limestone, Yorkshire, Belgium.]

21. Cyclus Tonesianus, H. W. Carboniferous Limestone, Little Island, Cork. (These latter figured and described in the Geol. Mag. 1870, vol. vii. pl. 23. figs. 1-9.)

[Those marked with an asterisk have been already figured, but have been redrawn and redescribed in order to add to or correct previous descriptions.

Thus, for example, “ Cyclus Brongniartianus” proves upon careful examination to be only the hypostome of a Trilobite belonging to the genus Phillipsia. Dithyrocaris tenuistratus is identical with Avicula paradoxides of De Koninck, &c.]

Since noticing the occurrence of an Isopod, Palæga Carteri, from the Kentish, Cambridge, and Bedford Chalk, Dr. Ferd. Roemer, of Breslau, has forwarded me the cast of a specimen of the same crustacean from the Chalk of Upper Silesia. This, together with the example from the Miocene of Turin, gives a very wide geographical as well as chronological range to this genus.

A still more remarkable extension of the Isopoda in time is caused by the discovery of the form which I have named Præarcturus in the Devonian of Herefordshire, apparently the remains of a gigantic Isopod resembling the modern Arcturus Baffinsii.

I have also described from the Lower Ludlow a form which I have referred with some doubts to the Amphipoda, under the generic name of Necrogammarus.

Representatives both of the Isopoda and Amphipoda will doubtless be found in numbers in our Palæozoic rocks, seeing that Macruran Decapods are found as far back as the Coal-measures*, and Brachyurous forms in the Oolitest.

Indeed the suggestion made by Mr. Billings as to the Trilobita being furnished with legs (see Quart. Journ. Geol. Soc. vol. xxvi. pl. 31. fig. 1), if established upon further evidence, so as to be applied to the whole class, would carry the Isopodous type back in time to our earliest Cambrian rocks.

I propose to carry out an investigation of this group for the purpose of confirming Mr. Billings's and my own observations, by the examination of a longer series of specimens than have hitherto been dealt with. In the mean time the authenticity of the conclusions arrived at by Mr. Billings having been called in question by Drs. Dana, Verrill, and Smith (see the American Journ. of Science for May last, p. 320; Annals & Mag. Nat. Hist. for May, p. 366),' I have carefully considered their objections, and have replied to the same in the Geological Magazine for July last, p. 289, pl. 8; and I may be permitted here to briefly state the arguments pro and con, seeing they are of the greatest importance in settling the systematic position of the Trilobita among the Crustacea.

Until the discovery of the remains of ambulatory appendages by Mr. Billings in an Asaphus from the Trenton Limestone (in 1870), the only appendage heretofore detected associated with any Trilobite was the hypostome or lip-plate.

From its close agreement with the lip-plate in the recent Apus, and also from the fact of the number of body-rings exceeding that attained in any other group save in the Entomostraca, nearly all naturalists who have paid attention to the Trilobita in the past thirty years have concluded that they possessed only soft membranaceous gill-feet, similar to those of Branchipus, Apus, and other Phyllopods.

The large compound sessile eyes, and the hard, shelly, many-segmented body, with its compound caudal and head-shield, differ from any known Phyllopod, but offer many points of analogy with the modern Isopods I ; and

* Anthrapalæmon Grossartii, Salter, Coal-measures, Glasgow. *Paleinachus longipes, H. Woodw., Forest Marble, Wilts.

I It should always, however, be borne in mind that as the Trilobita offer, as a group, no fixed number of body-rings and frequently possess more than twenty-one segments, they

one would be led to presuppose the Trilobites possessed of organs of locomotion of a stronger texture than mere branchial frills.

The objection raised by Drs. Dana and Verrill to the special case of appendages in the Asaphus assumed by Mr. Billings to possess ambulatory legs, is that the said appendages were merely the semicalcified arches in the integument of the sternum to which the true appendages were attached.

A comparison, which these gentlemen have themselves suggested, between the abdomen of a Macruran Decapod and the Trilobite in question is the best refutation of their own argument.

The sternal arches in question are firmly united to each tergal piece at the margin, not along the median ventral line. If, then, the supposed legs of the Trilobite correspond to these semicalcified arches in the Macruran Decapod, they might be expected to lie irregularly along the median line, but to unite with the tergal pieces at the lateral border of each somite. In the fossil we find just the contrary is the case ; for the organs in question occupy a definite position on either side of a median line along the ventral surface, but diverge widely from their corresponding tergal pieces at each lateral border, being directed forward and outwards in a very similar position to that in which we should expect legs (not sternal arches) to lie beneath the body-rings of a fossil crustacean. The presence, however, of semicalcified sternal arches presupposes the possession of stronger organs than mere foliaceous gill-feet; whilst the broad shield-shaped caudal plate suggests most strongly the position of the branchiæ. In the case of the Trenton Asaphus I shall be satisfied if it appears, from the arguments I have put forward, that they are most probably legs—feeling assured that more evidence ought to be demanded before deciding on the systematic position of so large a group as the Trilobita from only two specimens*.

With regard to the embryology and development of the modern KingCrab (Limulus polyphæmus), we must await the conclusions of Dr. Anton Dohrn before deciding as to the affinities presented by its larval stages to certain of the Trilobita, such relations being only in general external form. Dr. Packard (Reports of the American Association for the Advancement of Science, August 1870) remarks, “ The whole embryo bears a very near resemblance to certain genera of Trilobites, as Trinucleus, Asaphus, and others;" and he adds, “ Previous to hatching it strikingly resembles Trinucleus and other Trilobites, suggesting that the two groups, should, on embryonic and structural grounds, be included in the same order, especially now that Mr. E. Billings has demonstrated that Asaphus possessed eight pairs of 5-jointed legs of uniform size.”

Such statements are apt to mislead unless we carefully compare the characters of each group. And first let me express a caution against the too hasty construction of a classification based upon larval characters alone.

Larval characters are useful guide-posts in defining great groups, and also in indicating affinities between great groups; but the more we become acquainted with larval forms the greater will be our tendency (if we attempt to base our classification on their study) to merge groups together which we had before held as distinct.

have, as a matter of course, been considered as belonging to a much lower group than the Isopoda, in which the normal number of somites is seven. Whilst admitting the justice of this conclusion, we do not think it affords any good ground for rejecting the proposition that the Isopoda may be the direct lineal descendants of the Trilobita.

* One in Canada and one in the British Museum, both of the same species,

To take a familiar instance: if we compare the larval stages of the Common Shore-Crab (Carcinus monas) with Pterygotus, we should be obliged (according to the arguments of Dr. Packard) to place them near to or in the same group.

The eyes in both are sessile, the functions of locomotion, prehension, and mastication are all performed by one set of appendages, which are attached to the mouth; the abdominal segments are natatory, but destitute of any appendages.

Such characters, however, are common to the larvæ of many crustaceans widely separated when adult, the fact being that in the larval stage we find in this group what has been so often observed by naturalists in other groups of the animal kingdom, namely, a shadowing forth in the larval stages of the road along which its ancestors travelled ere they arrived from the remote past at the living present.

If we place the characters of Limulus and Pterygotus side by side, and also those of Trilobita and Isopoda, we shall find they may be, in the present state of our knowledge, so retained in classification.

I.
Pterygotus (Fossil, extinct).

Limulus (Fossil, and living). 1. Eyes sessile, compound.

1. Eyes sessile, compound. 2. Ocelli distinctly seen.

2. Two ocelli distinctly seen. 3. All the limbs serving as mouth 3. All the limbs serving as mouthorgans.

organs. 4. Anterior thoracic segments bear 4. All the thoracic segments bear

ing branchiæ or reproductive ing branchiæ or reproductive organs.

organs. 5. Other segments destitute of any 5. Other segments destitute of any appendages.

appendages. 6. Thoracic segments unanchylosed. | 6. Thoracic segments anchylosed. 7. Abdominal segments free and well | 7. Abdominal segments anchylosed developed.

and rudimentary. 8. Metastoma large.

18. Metastoma rudimentary.

Trilobita (Fossil, extinct).

Isopoda (Fossil, and living). 1. Eyes sessile, compound.

1. Eyes sessile, compound. 2. No ocelli visible.

2. No ocelli visible. 3. Appendages partly oral, partly 3. Appendages partly oral, partly - ambulatory, arranged in pairs. ambulatory, arranged in pairs. 4. Thoracic segments variable in 4. Thoracic segments usually seven,

number, from 8 even to 28, free free and movable (animal and movable (animal sometimes sometimes rolling into a ball).

rolling into a ball). 5. Abdominal series coalesced to 5. Abdominal somites coalesced, and form a broad caudal shield,

forming a broad caudal shield, bearing the branchiæ beneath.

bearing the branchiæ beneath. 6. Lip-plate well developed. 16. Lip-plate small.

Should our further researches confirm Mr. Billings's discovery fully, we may propose for the second pair of these groups a common designation, meantime we give the above as representing the present state of our knowledge.

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