516 Systematic Paleontology 



taxodont, the teeth arranged in an anterior and a posterior series; chon- 

 drophore subumbonal, trigonal ; pallial line interrupted by a shallow 

 sinus, due to the short siphons of the animal; inner ventral margins 

 simple. 



This genus also originated in the Paleozoic, but in the Silurian, one 

 period later than did Nucula. The eighty odd living species have a wide 

 geographic and bathmetric distribution, although the majority are boreal. 



A. Latitude of adult shell not exceeding 8 mm; outline trigonal, rostrum 



obliquely produced, obtusely angulated Leda whitfieldi 



B. Latitude of adult shell exceeding 10 mm, outline transversely elongated, 



rostrum squarely truncate Leda rostratruncata 



Leda whitfieldi n. sp. 



Plate XIX, Figs. 10-12 



yuculana pinnaformis Whitfield, 1885, Mon. U. S. Geol. Survey, vol. ix, p. 

 108, pi. xi, fig. 8. (Synonomy and fig. 7 excluded.) (Not Leda pin- 

 naformis Gabb, 1860.) 



Description. — Shell small, convex, cuneate dorsally, arcuate ventrally, 

 forming roughly a sector of 120° ; posterior end more produced than the 

 anterior and sharply rostrate ; anterior end evenly rounded ; umbones 

 inflated, flattened upon their summits; incurved, proximate; external 

 adult sculpture of twenty to thirty concentric rugse, strongest and most 

 crowded toward the ventral margin, altogether absent upon the umbones 

 and evanescent in the slightly depressed area directly in front of the 

 rostrum ; teeth fine but sharp, becoming increasingly finer and convergent 

 beneath the umbones ; both anterior and posterior series numbering from 

 tbirteen to seventeen ; ligament pit trigonal, minute, subumbonal : muscle 

 scars small, placed at the distal ends of the hinge; pallial line running 

 close to the ventral margin ; pallial sinus short, steeply ascending, squarely 

 truncate. 



Dimensions. — Altitude 3.7 mm. ; latitude 6.5 mm. 



Type Locality. — Haddonfield, New Jersey. 



Forms referable to Leda whitfieldi were included by Whitfield under 

 Leda pinnaformis Gabb, an error perpetuated by Weller and others. The 



