294 University of California Publications in Geology [Vol. 9 



but it differs from that species in being natter and in being more 

 inequilateral. If the hinges are compared, it is found that the 

 arms of the left cardinal of 8. planulata are of nearly equal length 

 whereas those of 8. falcata are markedly uneven. The length of the 

 type is equivalent to 38 mm. The dimensions of the specimen 

 figured in this paper are : length, 45 mm., height, 32 mm., con- 

 vexity, 7 mm. 



The type of this species was described from a Recent specimen 

 obtained from Santa Barbara, California. 



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



SPISULA MERRIAMI, n. sp. 

 Plate 27, figures 3a and 4 

 Shell small, trigonal, equivalve nearly equilateral, ventricose, 

 ornamented by numerous fine concentric ridges, which are more pro- 

 nounced and less numerous on the anterior and posterior dorsal 

 areas than upon the other portions of the shell ; beaks moderately 

 prominent, anterior dorsal area limited by a distinct ridge extending 

 from the umbo to the anterior extremity ; the margin of this area is 

 nearly straight ; posterior dorsal slope slightly convex, limited by an 

 indistinct ridge which extends from the beak to the base of the shell ; 

 anterior extremity more sharply pointed than the posterior ; base very 

 broadly rounded. Hinge plate relatively broad, chondophore oblique, 

 shallow, apically roofed by a broad flat spur ; left cardinal prominent, 

 high, arms broad, extending from the dorsal to the ventral margin 

 of the plate ; ventral sinus narrow, flat ; right cardinal with a prom- 

 inent anterior arm and a well-developed, although relatively thin 

 posterior arm ; laminae long, distant from the beaks ; anterior lateral 

 formed from the margin of the plate, top rounding, distant from the 

 anterior arm of the cardinal ; posterior lateral also with a rounding 

 top, dorsal and ventral slopes nearly equal ; anterior ventral lamina 

 formed from the upturned edge of the hinge plate, not confluent with 

 the anterior cardinal arm ; anterior dorsal scarcely developed, con- 

 siderably smaller than the corresponding posterior one. The dimen- 

 sions of the type are : length 18.6 mm., height 14.2 mm., convexity 

 4 mm. 



This trigonal species might be confused with the Cretaceous 

 form, 8. ashburnerii. It differs from that species in being less 

 tumid, in being more strongly sculptured and in the possession of 

 the posterior arm of the right cardinal. 



