315 Bulletin 5 45 



FOSSIL SHELLS. 139 



minent, not remote : base widely but not deeply 

 contracted, nearly parallel with the hinge margin : 

 anterior and posterior margins obtusely rounded : 

 series of teeth rectilinear, uninterrupted, decurved 

 at the tips ; space between the beaks with nume- 

 rous grooves proceeding from the teeth : inner 

 margin not very distinctly crenated : muscular im- 

 pressions elevated, and forming a broad line each 

 side, from the cavity of the beak to the margin. 



Length nine-tenths of an inch, breadth nearly 

 one inch and a half. 



3. A. incite. PI. x. fig. 3. Shell transversely 

 rhomboidal, with about twenty-seven ribs ; ante- 

 rior hinge margin compressed and angulated. 



Description. Disk prominent from the beaks 

 to the anterior part of the base : ribs with trans- 

 verse granules ; those anterior to the middle alter- 

 nating with very slender and but little prominent 

 lines, and with a groove on each : anterior margin 

 longer to the base than the posterior end, and con- 

 tracted in the middle : series of teeth nearly rec- 

 tilinear, entire ; interval between the teeth and 

 the apices with a few transverse lines or wrinkles ; 

 a single oblique groove from the apex to a little be- 

 fore the middle, and six or seven narrow ones from 

 the teeth outwards behind the apices : beaks placed 

 very far backward : inner margin crenated : mus- 

 cular impressions a little elevated, posterior one 

 short : basal margin not parallel with the hinge 

 margin. 



[J. A. N. S., Phila., ist Ser., Vol. IV," 1824.] 



