CRASSIPEDES. 125 



CRANIA. (Cranium, a skull.) Fain. Rudistes, Lam. Order, 

 Pallio-branchiata, Bl. — Descr. Inequivalve, equilateral, irregular, 

 sab-quadrate; upper valve patelliform, conical, with the umbo 

 near the centre; lower valve attached by its outer surface; mus- 

 cular impressions, 4 in each valve; two large, posterior, dis- 

 tant; two small, near to each other, central. No hinge teeth; 

 no ligament. — Obs. This genus properly belongs to the Brachio- 

 poda, Lam. It differs from Orbicula in the mode of attachment, 

 which in the latter, is by a byssus passing through the lower 

 valve, and not by the valve itself. Hipponyx has only two mus- 

 cular impressions in each valve. The name of this genus is de- 

 rived from the inner surface of the attached valve, which presents 

 a remarkable resemblance to the facial portion of a human skull. 

 This appearance is caused by the situation and elevated edges of 

 the muscular impressions. Fig. 197- Coasts of Britain and 

 Mediterranean. 



CRASSATED. (Crassus, thick.) Used to express a thickness in 

 the substance of a shell. Ex. Glycimeris, fig. 67. 



CRASSATELLA. Lam. (Crassus, thick.) Farn. Mactracea, Lam. 

 Conchacea, 31. — Descr. Equivalve, inequilateral, close, thick, 

 rounded anteriorly, rostrated posteriorly, with denticulated mar- 

 gins, smooth, or ribbed transversely ; hinge with a triangular pit 

 containing the cartilage, two anterior cardinal teeth, and a pos- 

 terior depression in one valve ; one anterior tooth and a slight 

 anterior marginal elevation, and a posterior elevation in the other 

 valve. Muscular impressions distant, strongly marked. Palleal 

 impression not sinuated. — Obs. The few recent species known 

 are marine, several being brought from the coasts of New Holland. 

 Fossil species are found in Calcaire-grossier and London clay. 

 The Crassatella are known from the Veneres, &c, by the liga- 

 mentary pit in tiie hinge, and from Lutraria and Mactra by the 

 thickness and closeness of the shell. Fig. 84, C. rostrata. 



CRASSINA. Lam. Astarte, Sow. 



CRASSIPEDES. Lam. {Crass us, thick ; pes, foot.) The first 

 section of the order Conchifera Dimyaria, Lam. In this section 

 the foot of the animal is thick, and the shell gapes considerably. 



