170 CONCHYLI A— D/THYi?^. 39. 



distant, witla a black striate oblong space between them; inside 

 blueish-white, ribbed longitudinally. 



39. PECTUNCULUS— L^lM^lKCiir. 



Testa suhorhicularis, eequivalvis, subcequilateralis, clausa ; umbonibus 

 conniventibus, estate gradatim remotioribus. Cardo arcuatus, denti- 

 bus numerosis obtusis alternatim insertis, centralibus obsoletis ; later- 

 alibus nullis. Ligamentum externum. 



Shell mostly orbicular, equivalve, generally equilateral, closed ; the 

 beaks close together, but becoming gradually more remote by age. 

 Hinge in a curved line, with numerous obtuse teeth alternately 

 closing together, the central ones obliterated : lateral teeth none. 

 Ligament external. 



The rounded outline of this genus, causing the hinge to form the 

 segment of a circle, instead of being placed in a straight line, na- 

 turally separates it from the Area. The species are all inhabitants 

 of the deeps, far more remote from the shores than the Cardium 

 and Venus tribes, and are not attached by a byssus, like most if not 

 all of the Area family. All have the inner margin notched. 



