1916] 



Packard: Mesozoic and Cenozoic Mactrinae 



279 



The dimensions of the specimen figured are : length 33.5 mm., 

 height 23 mm., convexity 6 mm. 



The lack of the suleate beaks, the more pronounced gape, the 

 more ventricose form, besides several details of the hinge will serve 

 to separate this species from Mactra calif or nica, with which it is 

 often associated. 



This Recent species was described from a specimen obtained from 

 San Pedro, California. The species is not certainly known to occur 

 in beds older than the Recent. 



Occurrence. — Recent : San Pedro, California, to West Colum- 

 bia. (Dall). 



Section Simomactra Dall, 1894 

 Type Mactra dolabriformis (Conrad) 

 Laminae lacking accessories. 



MACTRA DOLABRIFORMIS (Conrad) 

 Plate 12, figures 3a, 3b and 3c 

 Spissula 1 ® dolabriformis Conrad, Am. Jour. Conch., vol. 3, p. 193, 1867. 

 Spisula dolabriformis (Conrad), op. cit., appendix, p. 44. 

 Mactra dolabriformis Conrad, Dall, Nautilus, vol. 7, p. 138, pi. 5, fig. 1, 

 1894; Keep, West Coast Shells, p. 105, 1911. 



This species was described from a Recent specimen obtained 

 from Panama. Neither figure nor dimensions of this specimen were 

 given. Dall in a redescription of this form gives the following 

 dimensions : length 90 mm., height 63 mm., convexity 13 mm. 



This species might be confused with Spisula falcata, from which 

 it differs in its mactroid type of hinge, more elongate shape and 

 more pronounced umbonal ridge. 



Occurrence. — Recent: San Diego, California to Panama (Dall). 



Section Micromactra Dall, 1894 

 Type Mactra calif ornica Conrad 

 Shell small with suleate beaks. 



is This spelling of the generic name is evidently a typographical error 

 since it is spelled correctly by the same writer in the appendix of the 

 same volume. 



