of lateral teeth, the valves gape and the ligament is fix- 

 ed in a deltoid cavity. Blainville unites Amphidesma 

 with Lucina and with Fimbria, Megerle, or Corbis, Cuv. 

 But Corbis has lateral teeth ; an exterior ligament, though 

 deeply seated ; and the palleal line is entire ; it therefore 

 does not belong to the Mactraceae of Lamarck. The lat- 

 ter remark is also true of Lucina, of which the ligament 

 is exterior, the palleal line entire, and the posterior mus- 

 cular impression is elongated. 



PLAtB XXVIII. 



AMPHroESMA TRANSVERSUM. 



SPECIFIC CHARACTER. 



Transversely short oval ; hinge nearly central. 



DESCRIPTION. 



Shell transversely short oval, nearly equilateral, com- 

 pressed, a little gaping : anterior and posterior margins 

 subequally rounded, the latter somewhat more obtusely 

 &o : basal margin regularly rounded, without any undu- 

 lation before : apex obtuse, but little prominent : cardinal 

 teeth two : fosset dilated fusiform, abruptly very narrow 

 at the beaks : lateral teeth none : posterior muscular irrh 

 pression very slender, and elongated. 



