Clark: The San Lorenzo Series of Middle California 147 



It differs from this latter species in the following respects : it is not 

 so long in proportion to the height ; it is not so strongly truncated 

 posteriorly, and the lunule is not so sharply defined. 



MACEOCALLIST A ?, sp. 

 Plate 9, figure 1 



Several casts of a species which is apparently new were found at 

 University of California locality 14 ; the outline is rather elongate, 

 and the beaks fairly conspicuous. The posterior end is rather narrow 

 and acutely rounded ; there is no escutcheon ; the lunule is not pre- 

 served on any of the specimens at hand. The surface is covered by 

 fairly heavy, somewhat irregular lines of growth. The pallial sinus 

 reaches the middle of the shell, is strongly ascending and is bluntly 

 pointed. 



Genus PITARIA Romer 

 PITARIA LORENZANA, n. sp. 

 Plate 10, figures 2 and 4 

 Type specimen 11129, Coll. Invert. Palae. Univ. Calif., loe. 1131 

 Shell medium in size, fairly heavy, broadly subelliptieal to subovate, somewhat 

 variable in outline. Beaks well forward, prominent, strongly inturned. Anterior 

 dorsal slope steep, on the type specimen being almost at right angles to the anterior 

 part of the ventral edge; anterior end bluntly rounded; posterior dorsal edge long 

 and gently convex ; posterior end broadly and regularly rounded. Lunule fairly 

 large, lanceolate, slightly depressed and somewhat pouting along the dorsal edges. 

 Surface of shell covered by rather fine incremental lines, which on unweathered 

 specimens stand up as low but well-defined lamellae. Pallial sinus ample, strongly 

 ascending and pointed in front. Enough of the hinge plate was exposed to show 

 a well-defined anterior lateral in the left valve ; this, together with other char- 

 acters of the shell, appears to place it as belonging to the genus Pitaria. 



Dimensions. — Length, about 67 mm. ; height, 36 mm. ; maximum height of 

 posterior and beaks, 46 mm. ; diameter of both valves, 33 mm. 

 Occurrence. — University of California locality 1131. 



Pitaria lorenzana is rather similar to P. dalli "Weaver, 120 a char- 

 acteristic species of the Lower Oligocene of Washington, the 

 Molopophoms lincolnensis zone as recognized by Weaver. The sculp- 

 turing of P. lorenzana does not appear to be so lamellose as that 

 of the northern species, but this may possibly be due to the more 

 weathered condition of the specimens at hand ; on most of the speci- 

 mens of the northern form, examined by the writer, the anterior 

 margin is somewhat more produced, the posterior dorsal margin be- 



120 for original description of Pitaria dalli, see Weaver, C. E., Univ. Wash. 

 Publ. Geol., vol. 1, no. 1, pi. 1, figs. 1-4, 1916. 



