NUCULA. 



GENERIC CHARACTER. 



Shell transverse, equivalvcd, inequilateral; summits 

 contiguous; hinge with a primary, more or less triangular 

 fosset for the reception of the ligament, with an anterior 

 and posterior series of small, inserted, numerous, pectinate 

 teeth, interrupted at the summit by the fosset ; ligament 

 internal, very short, inserted into the fosset ; muscular im- 

 pressions two, simple. 



OBSERVATIONS. 



A genus connected with Area, Pectunculus, CucuUaia, 

 and Trigonia, but eminently distinguished by the ligament 

 being interior ; w hich, as has been remarked by Sowerby, 

 proves their relation to the Mactracca?. Many species are 

 known. Lamarck described six recent and the same number 

 of fossil species ; Sowerby four fossil and one recent ; De- 

 france enumerates twelve fossil, and we have published two 

 recent and two fossil species. Of all these the tellinoides, 

 Sowerby and lanceolata, Lam. appear to be the largest. 



The inhabitants are thus described by Blainville : Body 

 subtriquetrous ; mantle open on its inferior half only, the 

 margins entire, denticulated on the whole length of the 

 back, without posterior elongations ; foot very lai'ge, tliin 

 at its origin, dilated in a large oval disk, the mai'gins of 

 which are furnished with tentacular digitations ; anterior 



PLATE XII. 



