having also a few relatively bold furrows, or crenulations, between the centre of the convexity and the margin of the diaphragm. (Desc. Anim. Foss. Terr. Houill. &c., de la Belgique. Pl. B. fig. 6. c.)

Locality.Shoalhaven, Barbers, New South Wales. It is not possible to allude to the occurrence of a Favosites and an Amplexus, in Strzelecki's collection. without soliciting attention to the additional evidence they afford in support of previous inferences respecting the age of the deposits in which fossil polyparia were found by Mr. C. Darwin; or to the curious increase of agreement thus presented between the Paleozoic Fauna of Europe and extinct Fauna of New South Wales and Van Diemen's Land.

Fenestella ampla. (Pl. IX. fig. 3-3d.)

Cup-shaped; celluliferous
celluliferous surface internal ;

branches dichotomous, broad, flat, thin; meshes oval; rows of cells numerous, rarely limited to two, alternate; transverse connecting processes sometimes cellular; inner layer of non-cellular surface very fibrous; external layer very granular, non-fibrous; gemmuliferous vesicle? small." (Appendix to Mr. Darwin's work, p. 163.)

Among the specimens of this coral contained in the collection under consideration, was one which afforded some interesting changes dependent upon age, the absence of which in the series originally examined was alluded to in the notes upon the species. (Loc. cit. p. 165.) In the uppermost portion of this specimen, the casts of the cellular surface exhibited similar characters to those displayed in Mr. Darwin's series, with the addition, occasionally, of a crescent-shaped impression under the mouth, and due, it is believed, to a local modification of the sculpturing on the surface of the other cells. A little lower the ridges, or furrows representing them, began to disappear, and

still lower, by a further thickening of the exterior, all traces of them were obliterated, the interspaces between the mouths displaying irregular protuberances; and that which was considered as a state bordering upon decrepitude exhibited casts of minute oral apertures, with larger projections immediately beneath, marking the original extension of the mouths. Locality.-Spring Hill, Mount Wellington, Eastern Marshes, Van Diemen's Land.

Fenestella internata. (Pl. IX. fig. 2-2b.)

"Cup-shaped; celluliferous surface internal; branches dichotomous, compressed, breadth variable; meshes oblong, narrow; rows of cells 2-5, divided by longitudinal ridges; transverse connecting processes shut, without cells; non-cellular surface, inner layer sharply fibrous, outer layer minutely granular." (Appendix to Mr. Darwin's work, p. 165.)

Locality.-Mount Wellington, Van Diemen's Land; St. Patrick's Plains, Raymond Terrace, New South Wales.

66

Fenestella fossula. (Pl. IX. fig. 1, 1a.)

Cup-shaped; celluliferous surface internal; branches dichotomous, slender; meshes oval; rows of cells two; transverse processes non-cellular; inner layer of non-celluliferous surface minutely fibrous, external layer smooth or granular." (Op. cit. p. 166.) Locality.-Mount Wellington, Van Diemen's Land; St. Patrick's Plains, Raymond Terrace, New South Wales.

Hemitrypa sexangula. (Pl. IX. fig. 4, 4a.)

"Network fine, hexagonal; meshes round, in double rows." (Op. cit. p. 167.)

Locality.-Mount Wellington, Van Diemen's Land.

MOLLUSCA.

Mr. J. Morris, who furnished the preceding section, of Botany, with a valuable paper upon the Fossil Flora of New South Wales and Van Diemen's Land, has kindly favoured me with the following account of the fossil Mollusca found in my collection.

CONCHIFERA.

Allorisma curvatum. (Pl. X. fig. 1.)

Shell transverse, inequilateral, closed anteriorly, slightly gaping posteriorly, gibbose, front compressed, posterior side produced and incurved; beaks inflated, rounded, and approximate; surface concentrically marked with distinct but rather irregular sulcations, crossed by very faint radiating obtuse ridges; ligament large, external; posterior muscular impression distinct, anterior obscure; breadth 44 inches; length 3 inches.

This shell bears considerable resemblance to the Pholadomya Munsteri (D'Archiac and De Verneuil), but the anterior side is more obtuse, and the posterior less produced, than in that species, and slightly gaping; the folds on the surface are also much more irregular. It has the general form of Pholadomya, and might be included under the genus Homomya Ag., established for those species of Pholadomya in which the radiating costa are wanting, or not very prominent, if their absence alone could be considered sufficient for a generic division. I have provisionally placed this shell in the genus Allorisma (King), instituted for the reception of certain species of Sanguinolaria, as S. sulcata, S. elongata, &c., which have, according to that author, peculiar dental characters, and a more or less deep siphonal scar in the palleal impression.*

* Mr. Tate, of Alnwick, has kindly furnished me with a specimen of S. sulcata, showing clearly that the palleal impression was perfectly entire.

Sanguinolites (M'Coy) appears to be somewhat synonymous with Allorisma; but under that genus have been included some forms (S. contorta, &c.) having an entire palleal impression. Locality.-Illawara, New South Wales.

PACHYDOMUS (Taɣús crassus, dóμos domus).
Megadesmus (J. Sowerby).

Shell equivalved, inequilateral, very thick; hinge line sunk, with an antiquated area, and one or two (?) large teeth in each valve; ligament large, external; impressions of the adductor muscles very prominent, the posterior one larger than the anterior; retractor muscle distinct; palleal impression entire, broad, sometimes furnished with a very shallow sinus posteriorly; lunette more or less defined.

The above description is nearly similar to that given by Mr. J. Sowerby, in Sir T. Mitchell's work on Australia, for three or four species of very thick and rugose shells resembling Astarte in the character of the muscular impressions. The teeth have hitherto only been observed in imperfect casts of some of the species, from which it would appear that the one in the left valve is the largest, and thickened posteriorly; the muscular impressions are very deep, and the retractor muscle of the foot placed above the anterior adductor, is very distinct.

I have proposed the term Pachydomus, expressive of the thick shelly covering of the species constituting this genus, instead of Megadesmus, given by Mr. J. Sowerby, that generic title having been previously adopted by Bowdich for a genus of fluviatile Conchifera, named Galathea by Lamarck; Potamophila, G. B. Sowerby. The following species belong to this

genus:

P. antiquatus. Megadesmus antiquatus. (J. Sowerby, in Mitchell's Australia, Pl. I. fig. 2.)

Shell transversely elliptical, inequilateral, somewhat compressed; ligamental area oblique; lunette linear, deep.

Locality. Wollongong, New South Wales.

P. cuneatus. Megadesmus cuneatus. (J. Sowerby. Ibid. Pl. I. fig. 3.)

Shell somewhat trapeziform, very inequilateral, anterior side truncate, posterior rather rounded, front compressed. Mr. Sowerby observes, that this species differs from P. antiquatus only in having the shell a little contracted towards the anterior side.

Locality.-Wollongong.

P. lævis. Megadesmus lævis. (J. Sowerby. Ibid. Pl. I. fig. 1.)

Shell transversely oval, gibbose; umbones nearly central, anterior side rounded, posterior slope slightly depressed.

Locality.-Illawara, New South Wales.

P. globosus. (Pl. X. fig. 2, 3.)

Megadesmus globosus. (J. Sow. Ibid. Pl. III.)

Transversely obovate, ventricose, concentrically sulcated, anterior side small, slightly produced, posterior slope depressed; beaks approximate, incurved; breadth, 7 inches; length, 4 inches.

I had at first considered this shell as more nearly related to Allorisma than to Pachydomus, from some slight appearances of a sinus in the palleal impression: these markings, however, are very undefined; and this shell, having the general characters of the other