400 MOLLUSC A. 



the two valves, and lodging as many elastic ligaments; the irregular 

 and foliaceous shell marked on the anterior side and under the hinge 

 by a notch traversed by the byssus. The Pernae were also left by 

 Linnaeus among, the 03tre3e(l). 



Crenatula, Lam. 



The Crenatulae, lately separated from the Pernae, instead of hav- 

 ing transverse cavities on a broad hinge, are furnished with oval 

 ones on the very margin, where they occupy but little of its breadth. 

 The byssus seems to be wanting, and they are frequently found 

 among sponges(2). 



It is thought that we may approximate to the Pernae, certain fos- 

 sil shells, in which the hinge is also furnished with cavities more 

 or less numerous, that correspond to each other, and thus appear to 

 have furnished points of attachment to ligaments: thus those of the 



Gekvilia, Defr. 



Have a shell closely resembling that of the Volucells, but with a 

 kind of double hinge, externally with opposed cavities, receiving as 

 many ligaments, and internally furnished with very oblique teeth in 

 each valve. Their impressions are found along with Ammonites in 

 compact limestone(3). The 



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 lamellated texture(4). 



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 

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



(1) Ostrea isognomum, Chemn., VII, lix, 584; — 0. pema, lb., 580; — 0. legu- 

 men, lb., 578; — 0. ephippium, lb., Iviii, 576-^ — 0. mytilo'ides, Herm., Nat. Berl,, 

 Schr. II, ix, 9. 



(2) Ostrea piQta, Gm., Chemn., VII, Iviii, 575, or Crenatula phasionoptera, 

 Lam.j'Encyc. Method., Test., pi. 216, f. 2; — Crenatula avkularis. Lam., Ann. du 

 Mus, III, pi. ii, f. 3, 4; — Cr. mytilo'ides. Id., lb. f. 1 and 2. See also the great 

 work on Egypt, Coq. pi. xil. 



(3) Gervilia soleno'ides, Defi*., Blainv. , Malac, Ixi, 4. — G. perno'ides, Deslon- 

 champs, Soc. Lin. du Calvados, I, 116. — G. siliqua. Id. lb., &c. 



(4) Inoceramus concentricus. Parkins., Cuv., Oss. Foss., II, pi. vi, f. 11; — 

 Inocer. sukatus. Id., lb., f. 12. 



