292 NORTH-CAROLINA GEOLOGICAL SURVEY. 



FAMILY VENERIDA. 



This important family is represented by many existing 

 species in our seas at the present time. It is too well known 

 to require a minute description. It is, however, known from 

 other forms by its regular oblong thick shell, though it is 

 sometimes nearly round ; by its strong external ligament, and 

 its three diverging prominent teeth in each valve. Its pallial 

 line is sinuated. 



The venerida are elegant and beautiful shells, often highly 

 colored, though some of the best known are externally dull. 

 This family appeared first in the Oolitie period, and they have 

 increased in number and importance down to the present 

 time, when they have acquired their maximum develope- 

 ment. 



VENUS MERCENARIA. 



Shell solid, surface marked by numerous concentric lines 

 of growth, obliquely cordate ; posterior margin produced ; 

 anterior short ; umbones recurved, lunule cordate ; pallial 

 line sinuated ; margin crenulated. 



VENUS TRIDAENOIDES. CON. VENUS DIFFORMIS. SAY. 



Shell very tliiqk and heavy ; globose, wrinkles upon the 

 surface undulating ; plaits wide, extending from the urnbo to 

 the margin. 



This species may be distinguished by its thickness and wide 

 external plaits, which are usually strongly marked, though 

 sometimes they are feebly developed. It is one of the most 

 common fossils of the miocene beds of ^sTorth-Carolina. 



VENUS RILEYI. 



Shell large, thick, oblong, posterior margin prolonged, 

 anterior one short ; surface concentrically striate, and marked 

 by fine, longitudinal lines, which are distinct after the dermal 

 covering exfoliates. This is one of the largest species, being 

 sometims 6 7 inches wide. Common in the miocene of 

 Cape Fear river. 



