half a raised line t)arallel to rnd scarcely senarsted from the 

 outer edge of the area; anterior to the nraho is a similar, but 

 shorter area; external soul-pture of ver;; fine, inconspicuous, 

 impressed lines, obsolete in the umbonal and posterior regions and 



at ti^-es over the entire shell; ehondroTihore relativelj^ large; 

 teeth fine, the two series diverging at a very obtuse angle; 

 about eighteen teeth in the anterior and twenty in the posterior 

 series; anterior teeth larger, in both series the size reS.uced 

 gradually toward the point of divergence; muscle scars obscure; 

 pallia! line sharply, b-.t not dee-oly, sinuated. 



Dimensions .- length, 10.7 nm. ; alt,, G mm. ; semidiam. , 1.8 mm. 



Remarirs . - Jhe feebly impressed areas before and behind the 

 umbones are very narrow and inconspicuous. In the case of young 

 forms it may be better to describe the shell as having before and 

 behind the umbones a very narrow and shallow sulcus which impinges 

 on the dorsal mari^-iriS at approximately the dis^'al extremities of 

 ^he hinge, since on such forms the ridp-e just inside what is des- 

 cribee^ as the im.pressed areas in the adult is prominent enough to 

 caiise such an aopearance. The anterior and posterior marg-ins are 

 sir:ilsrly rounded, but the curve of the posterior mar^-in is more 

 complete since the posterior dorsal mars-in is less oblique than 

 the anterior. 



iEhe single Santo Domingian specimen is slightly more elong- 

 ated than the Bowden forms and has very feeble concentric sculp- 



