302 University of California Publications in Geology [ v °l- 9 



its possible affinities with S. falcata are the bases for the change of 

 genus as given above. 



This species is larger, relatively broader and more trigonal than 

 8. falcata. It differs from 8. brevirostraia in being more nearly 

 equilateral and from 8. albaria in being less ventricose. 



The type of this species was obtained in Waltham Creek Valley, 

 south of Coalinga, Fresno County, California. It was deposited in 

 the United States National Museum under the catalogue number 

 165513. 



Occurrence. — Pliocene : Etchegoin formation, Coalinga District, 

 California (Arnold). 



SPISULA LENTICULARIS (Gabb) 

 Hemimactra lenticularis Gabb, Pal. Cal., vol. 2, p. 19, pi. 4, fig. 3, 1869. 



This species was described by Gabb as follows : 



Sbell large, flattened, thin, inequilateral, irregularly subquadrate; beaks 

 eccentric, large, slightly curved forwards and inwards; anterior end broadly 

 concave below the beakt, and convex below; base and posterior end regu- 

 larly convex; cardinal margin sloping nearly straight. Hinge teeth slender. 

 Pallial sinus moderately deep, round at the base. Surface marked by irregu- 

 lar lines of growth. The dimensions of the type are equivalent to: length, 

 96 mm., height, 106 mm., convexity, 22.8 mm. 



The type of this species is apparently lost. The form will be 

 listed as a Spisula, since the genus Hemimactra as used by Gabb 

 has been reduced to the rank of a subgenus. Fragments of a large 

 form which may be referable to this species, have been collected 

 from the region of the type locality. 



The type locality of this species is given as ''South of Martinez, 

 Contra Costa County California." 



Occurrence. — Miocene: Contra Costa County, California (Gabb). 



SPISULA SISQUOCENSIS Arnold 



Spisula sisquocensis Arnold, Smithsonian Misc. Coll., vol. 50, p. 437, 

 pi. 56, fig. 1, 1907. 



This species was described by Arnold as follows : 



Shell averaging about 120 millimeters in longitude, subtrigonal in outline, 

 equivalve, inequilateral, ventricose; base regularly arcuate; beaks anterior, 

 prominent, bent forward, protruding beyond periphery of shell; anterior 



