198 PALEONTOLOGY OF CALIFORNIA. 



Localities: Abundant near Fort Tejon, and also found near Martinez. 



I bave been unable to discover tbe ligament area of tbis sbell ; wbich, if it 

 exist, must be unusually small. On one specimen, in wbich the hinge is par- 

 tially uncovered, there is an appearance which may prove to be the ligament pit 

 of the genus Limopsis. It is directly under the beak, and appears to produce an 

 interruption in the continuity of the teeth. 



A. COR, 11. S. 

 PI. 81, Fig. 2G8, and 268 a. 



Shell small, cordate, equivalve, widest below; base broadly 

 convex, sides nearly straight, diverging ; beaks small, prominent, 

 incurved; area small, narrow, impressed. Surface marked by 

 fine, elevated, radiating ribs, with broad, flat interspaces, crossed 

 by regular, concentric, impressed lines. 



Figure, twice natural size. 



Locality: Found only at Martinez, where a few specimens have been collected 

 by Mr. Mathewson. 



NUCULA, Lam. 



N. TRUNCATA, U. S. 

 PI. 26, Fig. 184, and 184 a, b. 



Shell moderate in size, oblique ; anterior end abruptly trun- 

 cated; posterior end produced, rounded; cardinal and basal 

 margins subparallel, convex; beaks small, anterior, terminal, 

 and nearly touching. Surface marked by divaricating ribs; 

 these ribs separate along an imaginary line, drawn from the 

 beaks to the posterior basal margin ; near the beaks they are 

 regular, but towards the base, especially near the posterior end, 

 they become irregular, sometimes diverging among themselves, 

 sometimes becoming dichotomous, and at times presenting a 

 "hacked" appearance, from the crossing of small impressed lines 

 at acute angles. Anterior end almost entirely occupied by a 

 large, sunken, subcordate lunule, faintly marked by minute ribs. 



