1915] 



Clark: Fauna of the San Pablo Group 



469 



on the posterior dorsal edge, which is nearly at right angles to hinge 

 plate. Lnnule large, elongate, slightly depressed, smooth. Surface 

 of shell sculptured by medium coarse to fine radiating ribs, the inter- 

 spaces between which are about equal to or slightly wider than the 

 tops of the ribs ; posteriorly and anteriorly the ribbing becomes finer 

 and closer together, becoming obsolete on approximately the posterior 

 one-fifth of the shell ; surface of shell also covered by rather heavy 

 concentric lines of growth. 



The sculpturing of this species resembles rather closely that of 

 G. securis Shumard, but the ribbing is finer and the beaks are not so 

 prominent. It differs radically in the outline and in the narrower 

 escutcheon. This species could very easily be mistaken for Papilla 

 staminea Conrad, a common species in the San Pablo also living on 

 the west coast. 



There is a very marked difference in outline between this species 

 and G. pabloensis, n. sp., also of the San Pablo Group; the radial 

 ribbing, however, is similar, as is also the escutcheon. 



Dimensions. — Length, 42 mm. ; height, 21 mm. 



Occurrence. — In the Upper San Pablo Group to the east of the 

 town of "Walnut Creek, University of California locality 1492. 



CHIONE PABLOENSIS, n. sp. 

 Plate 58; figure 2, also figure 1'? 



Shell elongate ovate to subtrigonal in outline : beaks prominent and 

 strongly incurved, about one-fifth the length of the shell from the 

 anterior end. Lunule large, not strongly depressed, sculptured only 

 by concentric striae; escutcheon strongly depressed and sharply de- 

 fined as an elongate area extending from the beak to very nearly the 

 ventral edge, concentrically striated only. Posterior dorsal edge long, 

 gently arcuate ; anterior dorsal edge short, gently concave ; ventral 

 edge long and regularly arcuate ; posterior end regularly rounded ; 

 anterior end regularly rounded, quite strongly produced. Ventral 

 edge and anterior dorsal edge crenulate. Surface sculptured by well- 

 defined radial ribbing, with interspaces as wide or wider than the tops 

 of the ribs; the radial ribbing is rather fine, and somewhat irregular, 

 becoming finer on anterior portion of shell and obsolete near the pos- 

 terior margin ; surface also sculptured by rather prominent incre- 

 mental lines ; the pallial sinus is fairly strong for this genus, and is 

 V-shaped. Hinge plate unknown. 



