74 CLASS I. TROPIOPODA. ORDER I. BIMUSCULOSA. 



The shell of Petricola is described as equivalve, inequilateral, trans- 

 verse, somewhat triangular or oblong, with the posterior side rounded ; 

 the anterior is more or less attenuated, and generally a little gaping. 

 The hinge is furnished with two teeth in each valve, either acute and 

 recurved, or short and obtuse. The ligament is external. 



Examples. 



PI. LI. Fig. 1 and 2. 



Petricola pholadiformis, Lamarck, Anim. sans vert., new edit., vol. vi. 

 p. 159. 



PI. LI. Fig. 3. 



Petricola dactylus, Sowerby, Genera of Shells, No. 15. 



PI. LI. Fig. 4. 



Petricola ochroleuca, Lamarck, Anim. sans vert., new edit., vol. vi. 



p. 157. 

 Tellina jragilis, Linnaeus. 

 Tellina ochroleuca, Wood. 



PI. LI. Fig 5. (fossil). 



Petricola rupestris, Sowerby, Genera of Shells, No. 15. 

 Venus rupestris, Brocchi. 



PI. LI. Fig. 6. 

 Petricola subglobosa, Sowerby, Genera of Shells, No. 15. 



Family 7. NYMPHACEA. 



Testa ad extremitates laterales raro subhians ; dentibus cardinalibus duo- 

 bus aut pluribus in eadem valva ; umbonibus prominulis. Liga- 

 mentum externum. 



This family was instituted bv Lamarck for the association of a nume- 



