142 Un iversity of California Publications in Geology [Vol.11 



Dosinia ponderosa Arnold, U. S. Geol. Surv., Bull. 309, pi. 33, fig. 47, 1907 ; 

 Proc. U. S. Nat. Mus., vol. 32, no. 1545, pi. 46, fig. 4, 1907, not Dosinia 

 ponderosa Gray. 



Dosinia whitneyi F. M. Anderson, Calif. Acad. Sci., ser. 3, vol. 3, p. 99, 



1911, not D. whitneyi Gabb. 

 Dosinia mathewsonii Gabb, Smith, Calif. Acad. Sci., ser. 4, vol. 3, pp. 



165 and 171, 1912. 

 Dosinia whitneyi, Arnold and Hannibal, Proc. Amer. Philos. Soc, vol. 52, 



no. 212, p. 588, 1913, not D. whitneyi Gabb. 

 Dosinia mathewsonii Gabb, Anderson and Martin, Calif. Acad. Sci., ser. 4, 



vol. 4, p. 41, 1914. 



Dosinia whitneyi Clark, Univ. Calif. Publ., Bull. Dept. Geol., vol. 9, no. 2, 

 p. 14, 1915, not D. whitneyi Gabb. 



This species is listed by Gabb as coming from the Miocene of Mar- 

 tinez, and at Griswold's on the road from San Juan to New Idria. 

 The type evidently came from the Agasoma gravidum beds near the 

 town of Martinez, Contra Costa County. The writer has been for- 

 tunate in finding good specimens, showing the hinge plates of both 

 valves of D. mathewsonii, from the Agasoma gravidum beds of Contra 

 Costa County and from the Lower Miocene of the Kern River section, 

 Kern County, California. The specimens from the Lower Miocene 

 of Kern River appear to be identical with those from the Agasoma 

 gravidum beds of Contra Costa County. In the right valve the 

 posterior cardinal, which is situated on the nymph plate, is long, 

 slender and low, and on some specimens is almost obsolete ; the poster- 

 ior of the two middle cardinals is long, fairly broad and high, with 

 a broad, rather deep groove. On the left valve the posterior and 

 anterior cardinals are narrow and slender ; the middle cardinal is 

 broad and heavy ; upon its upper surface there are two distinct ridges, 

 the posterior one being more prominent and longer than the anterior. 

 Anterior lateral short, fairly prominent. 



D. mathewsonii appears to be very closely related to D. elegans 

 Conrad, 118 an East Coast species, the range of which is from Upper 

 Miocene to Recent. In outline and sculpturing the two are very 

 similar ; the hinge plates are almost identical ; the chief differences 

 between them are that the anterior lateral in the left valve of D. 

 elegans is not so heavy and the posterior dorsal edge is apparently 

 sharper than on D. mathewsonii. Outside of these slight differences 

 it would be hard to differentiate the two species. 



us For original description of Dosinia elegans see Proc. Phila. Acad. Nat. Sci , 

 vol. 1, p. 325, 1843. 



