1914] Dicker son: Fauna of the Martinez Eocene of California 127 



Occurrence. University of California localities 1540 and 1580, 

 both being in the Trocliocyathus zitteli zone of the area north of Mount 

 Diablo. The Stanford University class in field geology, -1910, also 

 found this form in the Martinez just north of the Calabasas Quad- 

 rangle. This is the largest lamellibranch thus far reported from either 

 the Tejon or Martinez on this coast. 



Named in honor of my friend, Mr. R. S. Haseltine. 



OSTREA BUWALDANA, n. sp. 

 Plate 9, figure 4 



Shell, medium, with thick shell substance, only slightly oblique, 

 elliptical; upper valve flat; lower valve deep, convex and marked by 

 rough, squamose growth lines and about six strong radiating ribs. 

 Muscular scar is reniform, nearly central. Internal margins of some 

 specimens distinctly pitted on both sides of beaks in casts of this 

 species. Occasionally small tooth-like projections are seen on the 

 shell itself on both sides of the beaks. 



Dimensions. Length, 35 mm. ; height, 48 mm. ; convexity of lower 

 valve, 5 mm. 



Occurrence. University of California localities 790 near Lower 

 Lake and 693 at San Pedro Point, San Mateo County, California. 



It differs from 0. idriaensis Gabb in that the lower valve is marked 

 by radiating ribs. Its shape is more angular than that of 0. idriaensis. 

 The type is from University of California Locality 790. 



Named in honor of Mr. J. P. Buwalda. 



OSTKAEA WEAVERI, n. sp. 

 Plate 9, figure 3 



Shell medium in size, subequivalve, irregularly oval, contorted near 

 the beaks, unattached. Surface marked by regular squamose lines of 

 growth. Beak twisted and terminating at the anterior dorsal margin. 

 The upper half is subglobose while the lower half is flat or slightly 

 concave. These two portions are very deeply set off and the species is 

 readily determined by this characteristic. In the lower valve, the 

 bulging of the upper portion is less prominent. The growth lines are 

 remarkably even for this genus. 



