species belonging to the latter genus, has also been referred to the same.

Locality Illawara (New South Wales). Spring Hill (Van Diemen's Land).

P. carinatus. (Pl. XI. fig. 3, 4.)

Transversely ovate, elongated, very convex, rugose, posterior side more or less carinated, truncated at the margin, front slightly compressed, beaks prominent, about one third from the anterior margin; muscular impressions distinct, large, united by the entire palleal impression.

This species has considerable resemblance to the Cypricardia cordiformis, Deshayes, both as regards the general contour of the shell and the distinct muscular markings.

Locality. Illawara (New South Wales).

Orthonota? costata. (Pl. XI. fig. 1, 2.)

Shell elongate, inequilateral, cylindrical, rather compressed, posterior part traversed obliquely by twelve or fifteen prominent costæ, anterior portion small, rugose; beaks small, near the anterior extremity; muscular impressions very distinct, united by a simple well-marked palleal impression.

This is a very distinct species, and bears some general resemblance to Cypricardites corrugata, Conrad. Jour. Ac. Nat. Sc. Philadelphia, 8. t. 13. f. 1. The anterior portion is rugosely sulcated, the posterior obliquely traversed, beyond the umbonial slope, by twelve to fifteen costa; the muscular impressions are strongly defined, the anterior adductor being separated from the palleal impression by a slight thickening of the interior shell, producing a furrow in the

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cast, as shown in the figure; the lunette is small, somewhat lanceolate, with steep sides.

Locality. Illawara.

Orthonota? compressa. (Pl. XIII. fig. 4.)

Transversely elongate, very inequilateral, dorsal and basal margins nearly parallel; beaks very near to the anterior part, which is somewhat truncate, posterior end rounded; muscular impressions distinct, palleal impression entire.

This shell has somewhat the general form of Cardinia concinna, Ag., but wants the thick hinge of that species; the dental characters are very obscure. Locality. Spring Hill (Van Diemen's Land).

I have provisionally placed the two last-described shells in Conrad's genus Orthonota, from the general resemblance they present in external form to the species included under that generic title, rather than from any peculiarity in the dental character or situation of the muscular impressions, neither of which are mentioned by Mr. Conrad in his description of that genus. Unfortunately the dental and muscular characters of many of the Palæozoic bivalve testacea, (especially those species elongated in the direction of the hinge-line, with the dorsal and basal margins nearly parallel,) either have not been observed, or are but imperfectly known; without these characters it is certainly very difficult to arrange them systematically, and therefore, perhaps, the establishment of provisional genera may be of some service to palæontology, if only to place before us the numerous forms of the Palæozoic series; and therefore many of them are but arbitrarily located under genera to which they present only some analogy in external form. In the carboniferous limestone of England and Ireland, many forms are associated together, which

may ultimately be found to belong to very distinct genera. From the heterogeneous assemblage of species hitherto placed under Sanguinolaria, to which they certainly bear little affinity, Mr. King has, by a careful examination of the ligamental and muscular characters, abstracted a few species, with the generic title of Allorisma. Mr. M'Coy has included a larger number under his genus Sanguinolites (partly synonymous with Allorisma); and other somewhat similar forms, chiefly from the silurian strata of America, have been arranged by Mr. Conrad under the genera Orthonota and Cypricardites. The two species here provisionally placed under Orthonota, I am inclined to believe are very closely related to Sanguinolaria transversa, and S. undata Portlock, which latter forms, very probably, have an entire palleal impression, and may therefore be distinct from the true Allorisma, and considered worthy of a generic subdivision.

EURYDESMA (supús latus, deopós ligamentum).

"Testa æquivalvis, suborbicularis, tenuis, ad umbones crassissima, areâ ligamenti elongatâ, latâ, ferè omnino internâ, dente valvæ dextræ magno, obtuso, sinistræ inconspicuâ, canali byssifero antico ex umbonem ad marginem testæ decurrente; impressionibus muscularibus plurimis, parvis ex internam partem umbonis anticè decurrentibus."

At first inspection I was disposed to regard this shell as a relation of Isocardia; a more careful examination of all the specimens I have seen has, however, compelled me to entertain different views. I have ascertained that it really belongs to the Monomyaria, and that it ought to be arranged very near to Avicula, from which I believe it is only to be distinguished by its ventricose form and the position of

its great muscular impression, which, instead of being nearly central, as in Avicula, (including Meleagrina, Lam.) is placed anteriorly.

I have to acknowledge the kind assistance of Mr. G. B. Sowerby, to whom I submitted the specimens figured (Pl. XII.), for pointing out the peculiar characters, and interesting affinities of this genus, as well as for the above detailed generic description. Only one species of this genus is at present known, to which it is proposed to give the name of Eurydesma cordata.

E. cordata. (Pl. XII.)

Isocardia? (Mitchell's Australia, Pl. II. f. 1, 2.) Shell somewhat orbicular or cordiform, gibbose, nearly equilateral, surface radiately striate; beaks incurved, approximate.

This is a very ventricose and cordiform shell, the external surface being indistinctly radiately striated, a character which is well represented in the figure of this species given in Plate II. of Sir T. Mitchell's Expeditions into Australia. The ligamental area, dental characters, and small muscular impressions are carefully illustrated in Pl. XII. of the present volume. Locality. Illawara (New South Wales).

Pterinea macroptera. (Pl. XIII. fig. 2, 3.)

Obliquely spathulate, nearly convex, bilobed, smooth; anterior lobe small, posterior ear distinct, large, rectangular, hinge-line rather shorter than the shell.

This shell bears some general resemblance to those species placed in the genus Pteronites M'Coy. It has, however, a peculiar character: anterior to the beaks, in each valve, is a deep linear oblique pit or fissure, the

cast of a calcareous plate, or more probably of a tooth, which is not alluded to as being found in Pteronites, and does not exist in Avicula. By this character it is more nearly related to Pterinea, although the lengthened lateral teeth are not strongly defined.

Locality. Spring Hill (Van Diemen's Land).

Pecten Illawarensis. (Pl. XIV. fig. 3.)

Orbicular, depressed, smooth, with sixteen prominent rounded rays, slightly flattened in the centre; ears small.

This is a large and well-defined species, with very prominent rays, which are not quite so broad as the intervening furrows. It is very distinct from the generality of Palæozoic forms usually belonging to this genus.

Locality.Illawara (New South Wales).

Pecten limaformis. (Pl. XIII. fig. 1.)

Shell suborbicular, oblique, inequilateral, most convex towards the beak; rays numerous, irregular, approximate near the beak; ears rather small, wrinkled.

This is a very large and oblique species of Pecten, with about thirty-six obtusely angular ridges. Locality.-Eastern Marshes (Van Diemen's Land).

Pecten Fittoni. (Pl. XIV. fig. 2.)

Orbicular, wider than long, with about fifteen rounded rays, each bearing from three to five slightly elevated granular striæ; furrows equal in breadth to the ribs, and divided in the centre by a small ridge; ears equal.

Locality.-Mount Wellington (Van Diemen's Land).