3. P. Acharii, Ag.; filaments brownish-green, branched, erect; articulations twice or thrice as long as broad; joints contracted. Harv. l. c. p. 383. Conf. Acharii, Dillw. t. 69. On damp shady banks.

4. P. Orthotrichi, Ag.; filaments olivaceous, minute, branched, obtuse, erect; articulations about as long as broad. Ag. Harv. l. c. p. 383.. Conf. Orthotrichi, Dillw. t. 89. Conf. muscicola, E. Bot. t. 1638.

--

On the leaves of various Orthotricha; common.

5. P. muscicola, Ag. ; filaments brown, branched; branches alternate, divaricate, subulate; articulations thrice as long as broad. Harv. l. c. p. 383. Conf. castanea, Dillw. t. 72; E. Bot. t. 1701. Conf. muscicola, Web. and Mohr.

In shady places among mosses.

CVII. HYGROCROCIS. Ag.

Filaments colourless, interwoven into an uniform membrane or gelatine.-Name, vypos, belonging to water, and xponis, a little tuft. Obscure byssoid productions, found in chemical solutions and various infusions. They are probably, as Mr. Berkeley suggests, imperfectly developed moulds.

1. H. barytica, Ag. ; tufts globose; filaments very slender, cobwebby, colourless, densely interwoven, inarticulate, flexuous, branched; branches divaricating. Ag. Syst. p. 45; Loud. Encycl. Pl. No. 15087; Harv. l. c. p. 384.

In a solution of muriate of Barytes.

2. H. atramenti, Ag.; filaments dichotomous, branched, minute, decumbent, densely interwoven in a white stratum; articulations longer than broad. Ag. Syst. p. 48; Harv. l. c. p. 384.

On the surface of ink; very common.

3. H. typhloderma, Ag.; filaments slightly branched, densely interwoven in an olivaceous pellicle; articulations as long as broad. Ag. Syst. p. 46; Harv. l. c. p. 384. Conf. typhloderma, Dillw. t. 83.

In water containing a solution of gum dragon, Mr. W. W. Young.

4. H. pallida, Ag.; filaments dichotomous, curvato-flexuous, fastigiate, ochraceous, interwoven in a gelatinous, cori

aceous pellicle; axils rounded; articulations very long. Ag. Syst. p. 46; Harv. l. c. p. 384. Conf. pallida, Dillw. t. 78. "My friend Mr. W. W. Young having let some yellow ochre remain about a fortnight in a pot of isinglass size, found the surface of the ochre nearly covered by the present minute and interesting Conferva." Dillw.l.c.

5. H. Rosæ, Ag.; filaments colourless, slightly branched, interwoven into a cloud-like, olive-grey, bullated membrane, or compact, dull grey gelatine. Ag. Syst. p. 46.

In distilled rose-water, Miss Trevelyan.

6. H. sanguinea, Ag.; filaments branched, densely interwoven in a blood-red, gelatinous pellicle; branches divaricate; articulations rather longer than broad. Ag. Syst. p. 46; Harv. l. c. p. 384. Conf. sanguinea, Dillw. Conf. Syn. p. 55.

"Mr. Young discovered the present species, forming a densely matted membrane on the surface of some isinglass size, in which he had put some patent yellow to dissolve; but we have since repeatedly endeavoured to produce it in the same manner without success.” Dillw.

7. H. vini, Ag.; brownish-yellow; filaments colourless, interwoven, much branched; branches attenuate, acute; articulations twice as long as broad. Ag. Syst. p. 47; Harv. 1. c. p. 384; Loud. Encycl. Pl. No. 15093.

In Madeira wine.

CVIII. LEPTOMITUS. Ag.

Filaments colourless, erect, parasitical, growing in fresh water or in the sea.-Name, λɛπто5, slender, and μros, a thread.

1. L. minutissimus, Ag.; filaments slightly branched, very minute, colourless; branches scattered, forked, obtuse; joints imperfectly visible and of variable length. Ag. Syst. p. 47; Harv. l. c. p. 385. Conf. minutissima, Dillw. Conf. Syn.

t. F.

On the smaller Algæ, in the sea.

2. L. lacteus, Ag.; filaments branched, clustered in a shapeless, gelatinous mass, dirty white; branches from each dissepiment; articulations very long. Ag. Syst. p. 48; Harv. 1. c. p. 385. Conf. lactea, Dillw. t. 79.

In ditches and rivulets, chiefly such as contain a quantity of decaying vegetable matter.

3. L. clavatus, Ag. ; filaments simple, hyaline; apex clubshaped. Ag. Syst. p. 49; Harv. 1. c. p. 385.

aquatica, Lyngb. t. 22.

On fishes and dead flies.

Vaucheria

194

LEPTOMITUS-SCYTHYMENIA-MELOSEIRA.

4. L. pisidicola, Berk.; threads short, fasciculate, fastigiate; branches horizontal or even; the apices swollen, and containing a denser mass of granules than the rest of the plant. Berk. Gl. Alg. p. 30, t. 11, f. 1.

Growing on the putrefying body of Pisidium amnicum (Tellina amnica, L.), Rev. M. J. Berkeley.

CIX. SCYTHYMENIA. Ag.

Frond tough, leathery, spreading, its surface reticulated with raised, irregularly anastomosing veins; entirely composed of byssoid fibres, intermixed with granules.-Name, σxUTOS, leather, and unv, a membrane. This appears to me to be an unquestionable fungus, but whether described as such by authors I am unable to say.

1. S. rupestris, Ag. Syst. p. 30. Ulva rupestris, E. Bot. t. 2194, (not characteristic).

"On the nearly upright face of a rock, bathed with a perpetual trickling rill, at some distance above Fyloge bridge, near Hafod, 2 or 3 feet wide, spreading like a piece of very wet leather," Sir J. E. Smith.—In a dry state this curious production strongly resembles a piece of thickish, light brown leather. The upper surface is very prettily reticulated with raised, irregularly anastomosing veins, which form areolæ from 1 to 3 lines in diameter. Under the microscope it is found to be composed of densely packed, slender, byssoid fibres, irregularly connected, mixed with minute granules. I possess a specimen from Sir W. J. Hooker, who, I believe, obtained it from Sir J. E. Smith.

SERIES IV. DIATOMACEÆ.

TRIBE 23. DESMIDIEÆ.

Cylindrical or angular filaments, at length separating into segments, (frustula). Grev.

CX. MELOSEIRA. Ag.

Filaments cylindrical, very fragile, jointed, separating into single joints or frustula. -Name, hos, a membrane, and osipa, a chain; not exactly applicable, as the plant is not a string of membranes, but of cylindrical bodies.

* In fresh water.

1. M. nummuloides, Grev.; filaments fragile, very slender, nearly of equal diameter; joints about twice as long as

broad, containing a pair of globules which are either simple or divided by a transverse line. Grev. in Hook. Br. Fl. ii.

p. 401, (not of Agardh). M. discigera, Ag. Syst. p. 8, (omitted in Ag. Consp. Diat.) Conf. nummuloides, Dillw. Syn. p. 45, t. B.

Streams. Among the leaves of water-plants, in the river Lea at Walthamstow, Mr. Dillwyn. Near Margate, Rev. M. J. Berkeley.—Grey and powdery in a dry state.

2. M. lineata, Ag. ; filaments very fragile, nearly of equal diameter, dark brown; articulations 2 or 3 times as long as broad, at first containing a mass divided by a central line, afterwards this is separated into two globules. Grev. l. c. p. 402; Ag. Syst. p. 8, (omitted in Ag. Consp. Diat.) Conf. lineata, Dillw. Syn. p. 44, t. B.

Streams and ditches containing brackish or fresh water. In the river Lea, at Walthamstow, Mr. Dillwyn. Near Limerick, in fresh-water ditches.Filaments to an inch long, forming a dark brown stratum of considerable extent, ochre-coloured under the microscope. Is this distinct from the preceding ?

3. M. varians? Ag.; filaments very variable in diameter, fragile; joints once and a half to twice as long as broad, pellucid, or containing a dark ochrey mass divided by a transverse line. Ag. Consp. Crit. Diat. p. 64?

In a stream that issues from a coal-pit near Ballycastle, Co. Antrim, Mr. D. Moore.-This forms a brown cloud in the water. The filaments are extremely variable in diameter, some being more than twice as broad as others. When dry it is of a dull, greenish grey colour, without gloss, and powdery. I am not quite sure of the reference to Agardh, having seen no specimens of his plant. He describes the joints as usually about as long as broad, sometimes twice as long, and then marked with a band in the middle. I have only seen it in a dry state.

4. M. Thompsoni; filaments exceedingly slender, equal, brilliant yellow-green, glossy, very fragile; joints 2-4 times longer than broad, green in the centre, and having near each extremity a transparent globule.

Growing on stones in a mountain rivulet at Ballantrae, Ayrshire, Mr. W. Thompson.-Filaments attached, forming beautiful, glossy, dark green tufts. At the slightest touch they break into separate joints; and in a dry state preserve both their colour and lustre, a very unusual circumstance with plants of this group, and abundantly sufficient, were there no other marks, to distinguish this species from all its British congeners. It is not half the diameter of M. nummuloides; and there is a perfect equality among the threads. In this respect, and in the length of the joints, it approaches M. æqualis of Agardh (Consp. Diat. p. 64), but that plant is hyaline. I have much pleasure in dedicating it to its discoverer, from whom I have received many interesting plants and much valuable information, during the course of this work.

** In the sea.

5. M. Borreri, Grev.; filaments very fragile; the joints rather longer than broad, at length converted into a series of circular globules. Grev. 1. c. p. 401. M. nummuloides, Ag. Consp. Diat. p. 65. Conf. nummuloides, E. Bot. t. 2287, (not of Dillw.); Wyatt, Alg. Danm. No. 232.

Parasitic on marine filiform Algæ. Shoreham Harbour, and at Southwick, Mr. Borrer. Near the Land's End, Mr. Ralfs.—" The filaments of Mr. Borrer's plant are short, somewhat tortuous, and beautifully moniliform; greyish-green." Grev.

6. M. lentigera; filaments gregarious, affixed; joints strongly contracted, as long as broad, each containing two lenticular bodies. Rosaria lentigera, Carm. in Hook. Br. Fl. ii. p. 372.

On various small Algæ. Appin, rare, Capt. Carmichael.—“ Filaments gregarious, 1 or 2 lines in length, curved, of an olive colour, regularly contracted at equal distances to one fourth the diameter of the tube; cells as long as broad, containing two lentiform sporidia. At first the sporidia are in one mass, marked only by a transverse stria." Carm.

7. M. globifera; filaments scattered, affixed; joints twice as long as broad, slightly contracted, each containing two globular bodies. Rosaria globifera, Carm. l. c. p. 372.

On Enteromorpha percursa, Appin, extremely rare, Capt. Carmichael.— "Filaments scattered, 1 or 2 lines in length, of a fulvous colour, not above half the diameter of the preceding species. Cells slightly contracted, twice as long as broad, containing two globular sporidia." Carm.

CXI. DESMIDIUM. Ag

Filaments simple, angular, articulated, finally separating into single joints or frustula.-Name, deoμos, a bond.

1. D. Swartzii, Ag.; filaments triangular; the angles of the joints bicrenate. Grev. l. c. p. 402; Crypt. Fl. t. 292. In fresh-water pools and ditches, in spring and the beginning of summer. Appin, Capt. Carmichael." Plant forming a fine green, thin, gelatinous fleece. Filaments simple, about the thickness of the human hair, equal, flexible, an inch or more in length, triangular, more or less twisted, the angles pellucid and colourless, while the centre is green. Joints mostly half as broad as they are long, bicrenate at each of the three angles, separating from each other with facility. Before separation the two crenatures of each joint appear to contract, and the articulation to be dissolved from the circumference to nearly the centre, so that the filament has, for some time, a pinnatifid character." Grev. Crypt. Fl.

2. D. cylindricum, Grev.; filaments cylindrical, with two