50 CLASS I. TROPIOPODA. ORDER I. BIMUSCULOSA. 



daria and My aria ; we cannot but think, however, that it has a stronger 

 affinity with the Solenacea, and have therefore arranged it accordingly. 



Only one or two specimens of this curious molluscum are at present 

 known, and as we have not had the opportunity of seeing the shell in 

 good preservation, with the ligament entire, we give the original descrip- 

 tion of Sowerby: "Shell very thin, rather hyaline, transverse, ventri- 

 cose, inside pearly ; posterior side short, sometimes very short, rounded 

 anterior side more or less elongated, gaping ; upper edge also gaping a 

 little. Hinge with a small, rather elongated, triangular pit, and a mar- 

 ginal lamina in each valve, to the outer part of which is attached the 

 rather short external ligament. Muscular impressions two ; these, as 

 well as the muscular impression of the mantle, in which there is a large 



sinus, are indistinct." 



Example. 



PI. XXXII. Fig. 1 to 4. 



Pholadomya Candida, Sowerby, Genera of Shells, No. 19. Deshayes, 

 Enc. Meth., vol. iii. p. 756. 



Family 4. MYARIA. 



Testa ad utrumque latus plerumque hians, ligamento interno, in cavo 

 dentis prominuli, cochleariformi, inserto ; raro externo, appendice 

 testacea interdum partim connexo. 



The family of the Myaria form a very natural link between the Solena- 

 cea and the Mactracea, partaking of the characters of both. Their shell is 

 generally gaping on both sides, with the ligament internal, inserted in 

 the hollow of a prominent spoon-shaped tooth in one or both valves. It 

 is, however, sometimes external, partially covered with a small testaceous 

 appendage. 



Lamarck includes but two genera in his family of Myaria, viz. Mya 

 and Anatina, the latter of which we have found it necessary to divide, by 



