1916] 



Packard: Mesozoic and Ccnozoic Mactrinae 



283 



The type was obtained from University of California Locality 

 1237 : Top of knob about one-quarter of a mile south-east of Bur- 

 ton's and about one and one-half miles north of Los Trampas Creek, 

 Concord Sheet, Contra Costa County, California. 



Occurrence. — Miocene: San Pablo group. Contra Costa County, 

 California. 



Genus Spisula Gray, 1837 



Type Mactra solida (Linnaeus) Gray 



Shell generally small, nearly equilateral ; beaks adjacent ; dorsal 

 area not set off by a definite ridge or keel ; gape obsolete ; ligament 

 and resilium not separated by a shelly partition ; ligament sagitate, 

 partially external ; chondophore shallow, often roofed over by a 

 spur ; cardinal small and often overhanging the chondophore ; 

 anterior arm of the right cardinal is close to the dorsal margin of 

 the shell; laminae heavy, often grooved; pallia! sinus small, evenly 

 rounded ; epidermis thin. 



Subgenus Hemimactra Swainson, 1840 

 Type Mactra solidissima Dilliwyn 

 Plate 6, figures la and 16 

 Shell large, trigonal ; dorsal area not distinctly grooved ; teeth 

 somewhat concentrated ; cardinals small, compressed ; anterior arm 

 of the cardinal generally confluent with the ventral lamina ; the 

 laminae are often distinctly grooved. 



Section Mactromeris Conrad, 1868 



Type Mactra polynyma Stimpson 



Laminae smooth, ventral lamina not confluent with the anterior 

 arm of the cardinal. 



SPISULA VOYI (Gabb) 

 Plate 13, figure 4; plate 14 and plate 15 

 Callista voiji Gabb, Pal. Cal., vol. 2, p. 24, pi. 5, fig. 41, 1869. 

 Mactra ovalis Gould, Middendorf, Reise in den Aeussersten Norden und 

 Osten Siberiens, bd. 3, p. 363, 1843-1844. 



Spisula polynyma (Stimpson), Dall, Nautilus, vol. 7, p. 138, 1894. 

 Spisula polynyma (Stimpson) var. alaskana Dall, Nautilus, vol. 8, p. 

 40, 1894. 



Spisula alaskensis Dall, U. S. Geol. Surv. Prof. Paper, no. 59, p. 131, 1909. 

 Mactra (Spisula) alaskana Dall, Baker, Nautilus, vol. 24, p. 46, 1910. 



