CONCHOLOGY. 41 



2. Petricola. Thirteen species. 



This genus possesses the same faculty of boring rocks as 

 the Saxicava ; it is distinguished from the latter genus by 

 the hinge having one or two teeth in each valve. 



Shell sub-trigonal, transverse, inequilateral ; upper side 

 narrowed and a little gaping ; lower side rounded. 



Petricola lamellosa. Petricola rocelaria. 



P. ochroleuca. P. exilis. 



P. semilamellata. P. ruperella. 



P. lucinalis P. chamoides. 



P. striata. P. pholadiformis. 



P. costellata. P. labagella. 

 P. linguatula. 



P. lamellosa. The lamellous Petricola. PI. 7, fig. 3. 

 Species oval, trigonal, radiated ; two teeth on one valve, 

 and one on the other. 



P. pholadiformis. The Pholas-shaped Petricola. 

 Species transversely elongated. 



3. Venerirupis. Seven species. 



Another lithophagous shell, taken from the genus Venus, 

 from which it is distinguished by the different disposition of 

 the teeth, having three primary in one of the valves at least. 



Shell more or less irregular, sub-trigonal, striated or radi- 

 ated, equivalve, inequilateral, the anterior side shorter and 

 rounded, the posterior sub-truncated ; summits well marked ; 

 hinge sub-regular, more or less dissimilar, formed by slender, 

 narrow, cardinal teeth, variable in number on each valve, 

 sometimes two on the right and three on the left, and some- 

 times three on both ; these teeth are small, contiguous, par- 

 allel, and but little, if at all, divergent exterior ; very weak. 



Venerirupis perforans. Venerirupis exotica. 



V. nucleus. V. distans. 



V. irus. V. crenata. 



V. carditoides. 

 F 



