19161 Packard: Mesozoic and Cenozoic Mactrinae 301 



SUBGENERIC POSITION UNCERTAIN 

 SPISULA CALLISTAEFORMIS Dall 



Spisula callistaeform is Dall, Harriman Ala. Exped., vol. 4, p. 108, pi. 9, 

 fig. 9, 1904. 



Dall described this species as follows : 



Shell elongate, recalling Macrocallista in outline, the anterior end slightly 

 shorter, attenuated in front, arcuate below, wider and rounded behind with 

 an obscure radial ridgo near the dorsal slope; disk slightly flattened, con- 

 centrically striated, the beaks pointed and moderately elevated. . . . This 

 species is rather abundant and uniform. The pallial sinus is deep and 

 free from the pallial line for most of its length below. The dimensions 

 of the holotype specimen are: length, 50 mm., height, 28 mm., con- 

 vexity, 8 mm. 



This species is based upon fossil specimens obtained from the 

 eastern side of Chiehagof Cove, Alaska. The holotype was depos- 

 ited in the United States National Museum under the catalogue num- 

 ber 164882. 



Dall suggests that this species may belong to the subgenus Cym- 

 bophora. Specimens of this species have not been available for 

 study and therefore its subgeneric position is still uncertain. 



Occurrence. — Eocene: Upper Stepovak series, Alaska (Dall). 



SPISULA COALINGENSIS (Arnold) 

 Plate 27, figure 8 



Mactra coalingensis Arnold, U. S. Geol. Surv. Bull. 396, p. 71, pi. 25, 

 fig. 4, 1909. 



This species was described by Arnold as follows : 



Shell averaging about 52 millimeters in width, equivalve, trigonal in 

 outline, rounded behind, slightly attenuated in front; beaks not prominent, 

 situated slightly anterior to middle of shell; anterior superior margin only 

 slightly excavated in frcnt of beaks, nearly straight to anterior extremity, 

 which is quite abruptly truncated; posterior inferior margin slightly curved, 

 and merging imperceptibly into the regularly convex posterior extremity; 

 basal margin moderately curved. Hinge and cartilage areas concealed in 

 the type, but believed to be similar to M. falcata Gould. The dimensions 

 of the type are: length, 65 mm., height, 52 mm. 



Although several specimens that agree with the above descrip- 

 tion have been collected from the Etchegoin of the Coalinga District, 

 none has been found that shows the hinge. The general shape and 



