70 CLASS I. TROPIOPODA. ORDER I. BIMUSCULOSA. 



added by Lamarck under the title of Venerupis. This genus, as its name 

 implies, was made up of certain species of Linna?an Veneres, supposed 

 by him to possess the same property of terebrating as that which serves 

 to characterize the Lithophaga. Sowerby has, however, satisfactorily 

 shown that the Lamarckian Venerupes are merely cast into the cavities 

 in which they dwell by force of accident, and has accordingly removed 

 them from this family to that of the Conchacea. He there unites them 

 with certain other allied species of Linnsean and Lamarckian Veneres, 

 under the generic title of Pullastra, as will be seen in our observations 

 on that genus. The following are the two genera into which the Litho- 

 phaga are divided : 



Saxicava. 



Petricola. 



SAXICAVA, De Bellevue. 



Testa transversa, irregularis, plerumque oblonga, inaequilateralis, subin- 

 sequivalvis, latere antico hians. Cardo testee junioris dentibus 

 interdum duobus minutis, obtusis, indistinctis ; adultse obsoletis. 

 Ligamentum externum. Impressio muscularis pallii sinu nullo. 



The shell of Saxicava presents such a diversity of character at dif- 

 ferent periods of growth, that the same species has been assigned to two 

 or three different genera ; and even Lamarck has not escaped this im- 

 portant error ; for example, the Hiatella arctica of Daudin and Lamarck, 

 the Solen minutus of Chemnitz and Lamarck, the Mytilus rugosus of Lin- 

 naeus, and the Byssomya of Cuvier and De Blainville, are all one and the 

 same species, the Saxicava rugosa. In the young state, when covered 

 with small spines, it is the Hiatella arctica ; still younger, it is the Solen 

 minutus ; but in a more advanced state, when the spines are lost, the 

 teeth become obsolete, and the shell altogether assumes an irregular 



