- 1;'4 - 



ing the anterior ribs; the sculpture is similar on both valves; 

 the anterior end of the shell is rounded, the base arcuate, the 

 posterior end oblique above axA produced belov?; the ends of the 

 hinge-line are angulate^^; the cardinal area is moderately wide with 

 about three concentric lozenp-es o-;tlinerl by the grooving; the 

 hinge-line is straight, the teeth numerous snd mostly vertical, 

 the two series not interrupted., the posterior distal teeth tending 

 to become irregular in the adult. long, of shell 55, of hir^^re- 

 line 41, alt. 40, dian. 40 nm. ; large S'^ecimens reach a length of 

 68 mm." (Dall, 1898). 



? yp e locality .- Bow den, Jamaica, 



Angle between the ant erib-dorsal margin and the antero-later- 

 al margin almost 90°, that between the postero-dorsal and postero- 

 lateral about 125°; anterior radial ribs about equal to the inter- 

 spaces, but the ' posterior ones broader; in the anterior portion 

 of the shell the ribs have a relatively broad and deep sulcus 

 which extends half of the distance from the raar.sin to the umbo; 

 toward the central portion of the shell the sulcus occupies only 

 the distal third or fourth of the ribs and becomes progressively 

 shallower and narrower until in the central portion of the shell 

 it is Lierely a sharp line (one or tv/o of vAiich may be present); 

 ribs immediately anterior to the posterior slope broader and hav- 

 ing three or four inconspicuous lines; those on the posterior 



