56 CLASS I. TR0P10P0DA. ORDER I. BIMUSCULOSA. 



ANATINELLA, Sowerby. 



Testa ovata, sequivalvis, subsequilateralis ; latere antico rotundato, pos- 

 tico subrostrato, subtruncato ; ligamento interno, processui cochle- 

 ariformi in utraque valva affixo, appendice testacea nulla ; dentibus 

 duobus cardinalibus in utraque valva ante processum positis. Im- 

 pressio muscularis pallii integra, sinu nullo. 



This new and interesting genus, which was introduced by Sowerby 

 under the above title, has a shell very similar in its general appearance 

 to that of Anatina ; there is, however, no testaceous appendage, and the 

 sinus in the muscular impression is also wanting. The shell of Anati- 

 nella exhibits many characters in common with that of Crassatella ; in 

 fact, some authors have considered that this genus might have been 

 placed with equal propriety in the family of Mactracea ; the extreme 

 tenuity, however, of the shell, when compared with the solid thickness 

 of that of the last-named genus, sufficiently indicates that their animals 

 are essentially different. 



The shell of Anatinella is ovate, nearly equilateral, with the anterior 

 side rounded, and the posterior somewhat beaked or truncated ; the liga- 

 ment is internal, inserted between two spoon-shaped processes, one in 

 each valve, and on the anterior side of each are two cardinal teeth. 

 The muscular impression of the mantle does not exhibit any sinus. 



Example. 

 PL XXXVIII. Fig. 1 and 2. 

 Anatinella Sibbaldii, Sowerby, Genera of Shells, No. 40. 



