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University of California Publications in Geology [Vol.12 



tendency to converge at the extremity of the petal. Inferior surface 

 nearly flat but with a slight concavity around the mouth. Peristome 

 pentagonal in outline. Periproct situated above the ambitus, and 

 below an overlianging rostrum ; transversely elongate in outline. 



Related forms. — This species is separated from Cassidulus {Rhyn- 

 ehopygus) ynezensis Kew by its more elongate-shaped test, and by its 

 pentagonal-shaped peristome. It closely resembles Cassidulus {Rhyn- 

 eJiopygiis) patelliformis (Bouve) in shape, but may be distinguished 

 by its posterior petals, which are not so nearly elliptical in outline. 



Geologic liurizon. — Vaqueros formation. Lower Miocene; associated 

 with Cassidulus (Rhynchopygus) ynezensis Kew and Terebratalia 

 keuncdyi ( ?) Dall. 



Locality. — Cotypes from Santa Ynez River district, immediately 

 east of Oso Creek, Santa Barbara County, California, Univ. Calif, 

 loc. 3132. 



CASSIDULUS (RHYNCHOPYtlUS) MEXICANUS Kew, n. sp. 

 Plate 39, figures 4a, 4?>, 4c 



Holotypc.—No. 11357 Univ. Calif. Coll. Invert. Pal. 



Test large. Measurements of holotype : anteroposterior diameter 

 71.4 mm., transverse diameter 61.6 mm., greatest height 26.8 mm. 

 Outline from above subelliptical ; somewhat broader behind, and more 

 Ijointed anteriorly. Upper surface regularly arched to the anterior 

 extremity and posteriorly as far as the anal projection of the test ; 

 summit anterior to the center of the test. Apical system slightly 

 anterior to the center of the upper surface, but behind the apex; 

 madreporic area small. Petals lanceolate, slightly open at their ends, 

 extending about five-eighths the distance to the ambitus ; of unequal 

 width, the anterior pair being the widest and the odd anterior one 

 narrower tlian the posterior pair, but of the same length. Poriferous 

 zones well develoj^ed and similar in all petals ; anterior zones of the 

 posterior pair of petals somewhat longer than the posterior zones ; 

 rows of pores in the zones not joining at their extremities. Periproct 

 transversely elliptical and of large size ; situated about one-third the 

 elevation of the test above the ambitiLs ; a slight anal projection 

 immediately above ; below the test slopes down to the margain, forming 

 a shallow anal groove of the same width as the periproct. Tubercu- 

 lation of the abactinal side consists of small scrobicular tubercles of 

 uniform size. Inferior surface not exposed. 



