288 University of California Publications in Geology [Vol. 9 



Pallial sinus deep, oblique to the ventral margin. The dimensions 

 of the type, which was a Recent specimen from San Diego, California, 

 were given as : length 120 mm., height 93 mm., convexity 25 mm. 



A considerable number of specimens of this species have been 

 available for study. The species appears to be quite constant as 

 regards the general shape as well as the dental armature. 



This species might be confused with 8. catilliformis. From that 

 species it is separable on the basis of its shape; longer laminae; 

 the separation of the anterior lateral from the arm of the car- 

 dinal ; and the more oblique type of pallial sinus. 



Occurrence. — Recent: San Pedro to San Diego, California (Dall). 

 Pleistocene: San Pedro (Arnold) ; Newport, California. 



SPISULA OCCIDENTALIS (Gabb) 

 Plate 23, figures 1, 2 and 3 

 ? Hemimactra occidentalis Gabb, Pal. Cal., vol. 2, p. 54, pi. 15, figs. 13 

 and 13a, 1869. 



This species was described by Gabb as follows: 



Shell thin, subovate, inequilateral; beaks small, closely approximating, 

 placed about two-fifths of the length from the anterior end, which is broadly 

 excavated above, and prominently, though narrowly rounded below; posterior 

 end convexly and obliquely sub-truncated; cardinal margin sloping and 

 nearly straight, base broadly and regularly convex; a moderately distinct 

 angle runs from the beaks to the posterior basal margin. Surface covered 

 by small but moderately prominent and pretty regularly placed lines of 

 growth. 



The hinge plate is wide ; chondophore deep and slightly roofed ; 

 left cardinal is somewhat broken, but the remaining portion shows 

 that the arms were of nearly equal length and that the tooth was 

 situated medially upon the hinge plate ; arms of the right cardinal 

 heavy, the anterior one not confluent with, nor in the same plane 

 with the ventral lamina ; laterals but imperfectly preserved, the 

 anterior one arising from the ventral edge of the hinge plate, and 

 distant from and not in alignment with the anterior cardinal arm ; 

 laminae short and low, the posterior ventral one being the largest ; 

 ventral sinus is restricted by an abrupt inbending of the ventral 

 margin of the hinge plate. Pallial sinus extends to the middle of 

 the shell. The dimensions of the type obtained by Gabb from 

 the vicinity of Martinez, Contra Costa County, California, were 

 given as equivalent to: length, 69 mm., height, 59 mm., convexity, 



