146 University of CaUj 'or nia Publications in Geology [Vol.11 



MACEOCALLISTA PITTSBURGENSIS Ball 



Meretrix (Callista) pittsburgensis Dall, Trans. Wagner Inst. Sci., vol. 3, 



pt. 5, pi. 36, fig. 22; pi. 43, fig. 15, 1903. 

 Macrocallista pittsburgensis Dall, Trans. Wagner Inst. Sci., vol. 3, pt. 6, 



p. 1253, 1903. 



Macrocallista pittsburgensis Dall, Arnold and Hannibal, Proc. Amer. Philos. 



Soc, vol. 52, p. 581, 1913. 

 Macrocallista pittsburgensis Dall, Weaver, Univ. Wash. Publ. Geol., vol. 1, 



no. 1, p. 28, 1916; Proc. Calif. Acad. Sci., ser. 4, vol. 6, no. 2, pp. 28, 



29, 35, 1916. 



Macrocallista pittsburgensis Dall is one of the most characteristic 

 species of the Oligoeene of the West Coast. The type specimen came 

 from beds along the Nehalem River, near the town of Pittsburg", Ore- 

 gon; these beds were first referred by Dall to the Oligoeene, later to 

 the Tejon (Upper Eocene). The species is also found in the Oligo- 

 eene of Washington, being listed by Weaver as one of the character 

 istic species of his Molopophorus lincolnensis zone, or Lincoln horizon ; 

 it is found in the Kreyenhagen shales to the north of Coalinga and 

 in Oligoeene beds near the south end of the San Joaquin Valley in 

 the San Emigdio Hills. It is also found in the Astoria beds to the 

 north of Mount Diablo, at University of California locality 78, where 

 it is associated with Acila shumardi, Yoldia oregona, Agasoma gravi- 

 dum, Molopophorus cf. biplicatus, etc. 



MACEOCALLISTA WEAVEBI, n. sp. 

 Plate 12, figures 4 and 7 

 Type specimen 11155, Coll. Invert. Palae. Univ. Calif., loc. 1131 



Shell medium in size, beaks in the anterior fourth strongly inturned and 

 slightly prosogyrous. Posterior slope fairly long, nearly straight ; anterior slope 

 short, straight ; area anterior to the beaks rather strongly excavated. Ventral 

 margin regularly arcuate ; posterior end obliquely subtruncate. Surface sculptured 

 by regularly spaced and rather deeply incised, concentric lines, between which 

 are finer incremental lines. Extending from the beaks to the lower angle of the 

 posterior subtruncate end is a fairly distinct ridge, the area posterior to which is 

 rather strongly depressed. Lunule faint, larger on right valve than on left, 

 marked off by slightly impressed lines. Escutcheon absent. Ligamental groove 

 a little over half the length of the posterior dorsal margin. 



Dimensions. — Length, about 33 mm.; height, 22 mm.; greatest diameter, in- 

 eluding both valves, 15 mm. Hinge unknown. 



Occurrence. — University of California locality 1131. 



M. weavcri is of the same general type as M. pittsburgensis Dall, 119 

 which is common in the lower Oligoeene of Oregon and Washington. 



no For original description of M. pittsburgensis see Trans. Wagner Inst. 

 Sci., vol. 3, pt, 6, p. 1253; pi. 36, fig. 22; pi. 43/fig. 15, 1903. 



