LUTRARIA. 



TESTA plerumque tenuis, eequivalvis, insequila- 

 tera, trans versim ovata vel oblonga, laterie 

 postico plerumque long'iore, liiante, antico liia- 

 tulo. Cardo dentihus, alterius valvaa duobus; 

 alterius tribus, quorum posticus tenuis, compres- 

 sus. Ligamentitm internum, foveolse dentibus 

 adject ae, deltoideae, obiiquse, intus prominentia 

 affixum. Impressiones musculares duae latera- 

 les, distantes; impressio pallii adhaerenti mus- 

 culi, sinu magno. 



Sufficiently distinguished from Mactra by the absence 

 of lateral teeth^ and the large sinus in the muscular im- 

 pression of the Mantle : and from Anatina, to which some 

 of its species bear a near resemblance^ by its internal 

 ligament : at the same time it must be observed, that 

 several of the shells of Lamarck's division, c Coquille orbi- 

 culaire ok trigone, have one on both sides, a lateral la- 

 mina almost in the shape of a tooth, which does not, 

 however, appear to answer the same purpose. From the 

 decided Mactrae to these last mentioned, there appears 

 to be an almost imperceptible transition ; so that we can- 

 not profess ourselves to be entirely satisiied with the se- 

 paration of these genera, while at the same time we are 

 convinced of the necessity ol distinguishing genera by 

 certain parts of the shells, independently of the animals, 

 although we still labour under great difficulty in deciding 

 upon what characters may and what may not be consi- 

 dered as generic, on account of our slight acquaintance 

 with the animals. 



