468 



University of California Publications in Geology [Vol. 8 



PIT ARIA STALDERI, n. sp. 

 Plate 53, figures 5 and 6 

 Shell elongate, subovate ; beaks prominent, strongly inturned. 

 Lunule large, well defined, depressed, wider on right valve than on 

 left. Anterior dorsal edge slightly concave, abont two-thirds the 

 length of the posterior dorsal edge ; posterior dorsal edge long, 

 straight; posterior end broadly rounded; anterior extremity quite 

 strongly produced, and evenly rounded ; ventral edge long and gently 

 arcuate. Surface of shell sculptured by medium coarse, irregular, con- 

 centric, fairly sharp incremental lines. Posterior cardinal tooth of 

 left valve long, situated on top of long, narrow nymph plate ; middle 

 cardinal high and thin ; anterior cardinal thin but not so prominent 

 as middle cardinal ; anterior lateral prominent. Posterior cardinal of 

 right valve long, situated on anterior edge of long nymph plate, 

 grooved toward anterior end; middle cardinal not prominent, slightly 

 bifid ; anterior cardinal very thin, situated close up to the middle 

 cardinal. 



P. stalderi differs from P. behri, found in the same horizon, in 

 being more elongate ; the anterior extremity is more produced ; the 

 ventral edge is less arcuate, the posterior extremity is broader, and 

 it lacks the strongly depressed area along the posterior dorsal edge, 

 the incremental lines of growth do not stand out so prominently or so 

 regularly as on P. behri. The hinge plates of the two species are quite 

 different. The middle cardinal tooth on P. behri, n. sp., is much 

 heavier, and the platform on which the anterior laterial rests on P 

 behri is wider than on P. staleleri. 



Named in honor of Mr. Walter Stalder. 



Dimensions. — Length of type (pi. 53, tig. 6), about 67 mm.: height, 

 52 mm. 



Occurrence. — From the Lower San Pablo Group on San Pablo 

 Bay, University of California localities 1279, 1532 and 1524. 



CHIONE DIABLOENSIS, n. sp. 

 Plate 58, figure 4 



Shell medium in size, roughly quadrate in outline ; beaks anterior 

 to the middle of the shell, fairly prominent, rather strongly inturned. 

 Posterior dorsal edge gently arcuate; anterior dorsal edge nearly 

 straight; posterior end subtruncate; anterior end evenly rounded; 

 ventral edge regularly arcuate. There is a long, narrow escutcheon 



