Clark: The San Lorenzo Series of Middle California 119 



Subkingdom MOLLUSCA 



Class PELECYPODA 



Family Nuculidae 



Genus ACILA Adams 

 ACILA GETTYSBUEGENSIS Eeagan 

 Plate 13, figure 9 



Nucula (Acila) gettysburgensis Eeagan, Trans. Kansas Acad. Sci., vol. 22, 



p. 175, pi. 1, fig. 3, 1909. 

 Nucula gettysburgensis Eeagan, Weaver, Wash. Geol. Surv., Bull. 15, p. 18, 



1912. 



Acila gettysburgensis Eeagan, Arnold and Hannibal, Proe. Amer. Philos. 



Soc, vol. 52, pp. 583, 584, 1913. 

 Acila gettysburgensis Eeagan, Weaver, Univ. Wash. Publ. Geol., vol. 1, 



no. 1, p. 28, 1916; Proc. Calif. Acad. Sci., ser. 4, vol. (5, no. 2, p. 35: 



ibid., no. 3, p. 51, 1916. 



The outline of Acila gettysburgensis Reagan is very similar to 

 that of Acila shumardi Dall, the most conspicuous difference between 

 the two being that on the outer surface of the former there is a 

 distinct sinus or groove, which extends from the beak to the ventral 

 edge and a little anterior to the posterior end. The shell is thicker 

 and heavier, the sculpturing somewhat coarser, and the escutcheon 

 more strongly depressed. 



ACILA MUTA, n. sp. 



Plate 13, figures 6, 12 and 13 



Type specimen 11196, Coll. Invert. Palae. Univ. Calif., loe. 1131 

 Shell subovate to subtrigonal, moderately convex; beaks strongly inturned ; 

 posterior end abruptly truncated, subangulate at point of junction between the 

 posterior dorsal and the ventral edges. Anterior dorsal slope long and gently 

 convex; posterior dorsal slope straight; apical angle about 90°; anterior end 

 evenly rounded; posterior ventral edge regularly arcuate. Lunide obsolete; 

 escutcheon large, well-defined by a circumscribed line, pouting in the middle. 

 Surface of shell covered by fine, divaricating threads which extend onto th- 5 

 escutcheon ; the line at which the divaricating threads cross, is near the middle of 

 the shell ; on some of the larger specimens, a duplication of the divarication may 

 be seen near the ventral edge. Seventeen or eighteen fairly prominent cardinals 

 anterior, and about ten posterior to the beaks ; resilium pit narrow and deep, 

 rather long. 



Dimensions. — Type specimen: length, 17.8 mm.; height, 10 mm. 



Occurrence. — A very common species in the Oligocene of Washington, Oregon 

 and California; found at University of California localities 14, 52, 199, 1131, 

 1173, 1312, etc. 



