284 University of California Publications in Geology t VoL - 9 



This species was described by Gabb as follows : 



Shell broad, inequilateral; beaks in advance of the middle; cardinal 

 margin nearly straight and sloping; anterior end very much produced, 

 rounded and narrow; posterior end obliquely truncated; base broadly and 

 regularly rounded. Surface marked by numerous irregular and rather 

 strong lines of growth. 



The hinge plate of this species is wide, the chondophore oblique, 

 shallow, very slightly overhung by the posterior arm of the cardi- 

 nal ; left cardinal heavy, high, situated on the dorsal portion of the 

 hinge plate ; arms heavy, of equal length, free from accessories, 

 ventral sinus excavated ; right cardinal low, anterior arm thick, 

 appressed to the shell margin ; posterior arm very thin ; anterior 

 lateral low, acutely pointed, its dorsal base extending back of, and 

 parallel to the anterior arm of the cardinal ; posterior lateral low, 

 long, reaching as an indistinct ridge nearly to the umbones ; pos- 

 terior laminae low and long ; anterior laminae very short ; dorsal one 

 arises from the margin of the shell. Pallial sinus of the Recent 

 specimens deep, rounded and oblique to the pallial line. This is not 

 shown in the plesiotype. The dimensions of the plesiotype are : 

 length 85 mm., height 60 mm., convexity 18 mm. 



This species was described from a fossil specimen obtained from 

 below Bear River, Humboldt County, California. Several speci- 

 mens from Eel River, Humboldt County, were labeled Callista voyi 

 by the State Geological Survey. One of these corresponds in outline 

 and size to Gabb's conventional figure. The hinge of this specimen 

 has been exposed. Its mactrine character was first recognized by 

 Dr. Merriam. 21 The complete dentition is now known from the 

 specimens obtained from the above-mentioned region. A study of 

 these together with the type shows that they are identical with 

 Spisxda alaskana of the Recent fauna. 



The hinge of this species might be confused with that of 

 8. catilliformis. It differs from that species in that the anterior 

 lateral is never fused to the anterior arm of the cardinal and that 

 the posterior laminae are much more elongate. 



The fossil forms are slightly more ventricose than are the few 

 available Recent specimens. The general shape of both the fossil 

 and Recent specimens varies considerably as regards the relative 

 lengths of the shells. 



21 Merriam, J. C, A list of the type specimens in the Geological Museum 

 of the University of California, etc., Berkeley, 1895. 



