1916] Packard: Mesozoic and Cenozoic Mactrinae 



297 



as follows: "Along the east bank of Eel River one mile north of 

 Scotia, Humboldt County, California." 



Occurrence. — Pliocene : Wildcat group, Humboldt County, Cali- 

 fornia. 



Subgenus Sy minor phomactra Dall, 1894 



Type Mactra falcata Gould 



Cardinals prominent, thin, posterior arm of the cardinal tooth 

 overhangs the chondophore ; accessories on each arm ; hinge plate 

 flat. 



SPISULA FALCATA (Gould) 

 Plate 26, figures la, lb and lc 

 Mactra falcata Gould, Proc. Boston Soc. Nat. Hist, vol. 3, p. 216, 1849. 

 Standella falcata (Gould), Gabb, Pal. Cal., vol. 2, p. 92, 1869. 

 Spisula falcata (Gould), Dall, Nautilus, vol. 8, p. 41, 1894. 



The shell of this species is small, subtrigonal, slightly inequi- 

 lateral. The beaks are small, sharply pointed and situated a little 

 posterior to the middle of the shell ; anterior dorsal edge nearly 

 straight ; posterior edge somewhat convex ; base gently arcuate ; 

 anterior extremity somewhat attenuated, posterior evenly rounded. 

 Hinge plate rather wide, chondophore shallow, apically roofed and 

 overhung by the posterior arms of the cardinals ; spur prominent ; 

 left cardinal fragile, compressed, the anterior arm much longer 

 than the posterior, which markedly overhangs the resilifer; anterior 

 arm of the right cardinal the heavier, bearing anteriorly a small 

 lamella; laterals rather short, smooth, arising from the ventral 

 margin of the hinge plate at a point distant from the umbones ; 

 laminae short, low and rather heavy, the dorsal ones arising from 

 the dorsal shell margin ; a prominent lamella occurs in the left valve 

 between the anterior lateral and the cardinal, being parallel to and 

 nearly equal in height to, the latter. Pallial sinus shallow, irregu- 

 larly rounded. The dimensions of the specimen figured in this 

 paper are : length, 43 mm., height, 31 mm., convexity, 7 mm. 



The Recent specimens studied show but little variation in gen- 

 eral shape. This species superficially resembles S. brevirostrata, 

 from which it has been recently separated. It differs from that new 

 species in being more elongate and in possessing the compressed left 

 cardinal characteristic of the subgenus Symmorphomactra, also in 



