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University of California Publications in Geology [Vol. 8 



This species is very closely allied to Chione securis Shumard {Venus 

 securis Shumard, Transactions St. Louis Acad. Sci., no. 2, p. 122, 1858 ; 

 also, U. S. G. S. Professional Paper, no. 59, p. 120, pi. XI, fig. 8 ; pi. 

 XIII, fig. 289). G. pabloensis differs from C. securis Shumard in 

 being more elongate ; the ribbing is finer and the escutcheon is more 

 sharply defined. 



Dimensions. — Height of shell, 53 mm. ; length of shell, 72 mm. ; 

 diameter of both valves, 35 mm. 



Occurrence. — Upper San Pablo Group on the south side of Mount 

 Diablo, University of California locality 1485. 



VENUS MABTINI, n. sp. 

 Plate 54, figure 1 



Shell medium in size, suboval, inequilateral, equivalved. Beaks 

 fairly prominent, strongly inturned. Lunule lacking but with an 

 obscure, elongate depressed escutcheon-like area along the posterior 

 dorsal edge. Anterior dorsal edge rather short, slightly concave ; pos- 

 terior dorsal edge long and nearly straight; ventral edge regularly 

 and gently arcuate ; posterior end broadly and evenly rounded ; an- 

 terior end evenly rounded. Surface of shell sculptured by heavy, 

 prominent, rounded regular concentric undulations with interspaces 

 averaging about as wide as the undulation. The interspaces and the 

 undulations are covered by fine incremental lines. The hinge plate 

 of left valve was exposed showing three well developed cardinals with 

 no anterior lateral. Pallial sinus unknown. 



This species resembles closely V. pertenuis Gabb in sculpturing 

 but differs quite radically in outline, the latter being more trigonal 

 and less elongate. V. pertenuis is common in the Lower Neocene and 

 in the Santa Margarita of the north of Coalinga. In the latter horizon 

 it is associated with V. martini. 



Named in honor of Mr. Bruce Martin, formerly Assistant Curator 

 of Palaeontology of the California Academy of Science, San Francisco. 



Dimensions. — Length, about 63 mm.; height, about 50 mm.; diam- 

 eter of both valves, 33 mm. 



Occurrence. — From the Upper San Pablo Group usually associated 

 with Astrodapsis whitneyi, University of California localities 181, 741, 



