i7° Bulletin 29 334 



what longer, slightly inclined and somewhat broken up; cardinal 

 area wide for the group, with about five concentric, somewhat ir- 

 regular grooves. Length Si, altitude 50, thickness of both 

 valves 49 mm. 



This species is superficially somewhat like A. secticostata 

 Reeve, but the ribs in that species are deeply grooved. 



Locality. — (Exp'd '16) Rio Cana, Guayubin to Mao road. 



Scapharca guayubinica , n. sp. 

 Plate 28, Figure 4; Plate 29, Figure 1 



Shell ventricose, ribs twenty-nine; beaks mesially impressed ; 

 cardinal area moderately wide with about four concentric grooves, 

 part of which do not extend ahead of a V-shaped groove connect- 

 ing the beaks, with the point turned backwards; hinge line long 

 with numerous teeth forming two series, the anterior vertical, 

 the posterior series about one and a half times as long, gradually 

 increasing in length posteriorly, the posterior teeth somewhat in- 

 clined. Length 45, altitude 31, diameter 29 mm. 



This species is very similar to A. Margaretce excepting that 

 the hinge is comparatively wider and the shell only half as large. 

 Specimens in our Gabb collection appear to be mature and a 

 valve of ours from Rio Cana, 53 mm. in length, has every ap- 

 pearance of an aged shell, while A. Margarets though twice as 

 large does not appear senile. 



Locality. — (Exp'd '16) Rio Cana, Guayubin to Mao road. 



Scapharca riogurabonica, n. sp. 



Plate 29, Figure 4 



We collected a number of similar valves identical with one 

 in the Gabb collection, which like the preceding was in Gabb's 

 box of "Area consobrina" . This species is smaller than A. 

 guayubinica and more produced along the umbonal ridge, with a 

 more marked angle between the posterior and ventral margins; 

 it is less inflated anteriorly. In A. guayubinica the anterior and 

 . basal margins are distinct and meet in a broad curve, while in 

 the species now described the two tend to form a point near the 



