90 J1OLLUSCA. 



INOCERAMUS, Sowerb. 



Is remarkable for the elevation and inequality of the valves, the 

 summit of which curves in a hook towards the hinge, and which has 

 a lamellatcd texture *. 



CASTILLUS, Brong. 



Independently of the depressions for the ligament, the Castilli are 

 marked by a conical sulcus, sunk in a lip, which is bent at a right an- 

 gle to form one of the margins of the shell. The valves are about 

 equal, and of a fibrous texture. They appear to have had a byssus f. 



PULVINITES, Defr. 



A regularly triangular shell, in which the few depressions diverge 

 from the summit on the inside. The impression is found in chalk J. 



In the second subdivision of the Ostracea, as well as in almost all 

 the bivalves which follow, besides the single transverse muscular mass 

 of the preceding genera, there is a fasciculus which is placed before 

 the mouth, and extends from one valve to the other. It is apparently 

 in this subdivision that we must place the 



ETHERIA, Lam. 



Large inequivalve shells, as irregular as those of the Ostrese, and more 

 so ; no teeth to the hinge ; the ligament partly external and partly 

 internal. They differ from the Ostreae in having two muscular im- 

 pressions. The animal is not seen to produce a byssus , 

 They have lately been discovered in the Upper Nile ||. 



AVICULA, Brug. 



An equivalve shell with a rectilinear hinge, frequently extended into 

 wings by its extremities, furnished with a narrow and elongated liga- 

 ment, and sometimes with small notches near the mouth of the ani- 

 mal ; in the anterior side, a little beneath the angle of the side of the 

 mouth, is a notch for the byssus. The anterior transverse muscle is 

 excessively small. 



The species with less salient ears form the PINTADIN^E, Lam., or 

 MARGARITA, Leach. 



The most celebrated, Mytilus margaritiferus, L., Chemn., VIII , 

 Ixxx, 717> 721, has nearly a semicircular shell, greenish without, 



*^Inoceramus concentricus, Parkins., Cuv., Oss. Foss., II, pi. vi, f. 11 ; Inocer. 

 sulcatus, Id., Ib., f. 12. 



f Catillus Cnvieri, Brong., Cuv., Oss. Foss., II, pi. iv, f. 10. 



J Pulvinitcs Adansonii, Defr., Blainv., Malac., Ixii, bis, 3. 



Etheria elliplica, Lam., Ann. clu Mus. X, pi. xxix, and xxxi ; Elh. fngonula, 

 Ib., pi. xxx ; Eth. seminularis, Ib., pi. xxxii, f. 1, 2; Elh. transversa, Ib., f. 

 3, 4. 



|| Eth. Caillaudi, Voy. de Caillaud a Mdro<>, II, pi, lxi,-f. 2, 3. 



