134 THE NAUTILUS. 



tinged with greenish. Periostracum thin, shghtly glossy, 

 closely adhering. 



Nacre anteriorly lustrous white and thickened, posteriorly 

 thin, violaceous and brilliantly iridescent. Pallial line not 

 sharply defined and with several concentric striae above it, its 

 anterior portion radiately striated. Anterior adductor and 

 retractor scars separated, deep and rough, posterior scars super- 

 ficial. Dorsal muscle scars concealed by the incurving of the 

 upper portion of the valve. 



Lateral tooth of right valve thin, very high, wing-like, stri- 

 ated longitudinally. Laterals of left valve similar to that of 

 right valve, but smaller, the groove between them being very 

 narrow. Pseudocardinals of right valve two, thin, opposite, 

 the upper one being the stronger. Pseudocardinals of right 

 valve coalescing, standing in the same straight line, the anterior 

 one high, slightly curved, the posterior low, its summit irregu- 

 larly crenulated. The sculpture of each umbo consists of four 

 concentric ridges, highest (almost a nodule) at their posterior 

 ends, and numerous concentric striae. 



The type U, S. National Museum, Cat. No. 215130 comes 

 from the James River at Huron, South Dakota, and was col- 

 lected by the U. S. Bureau of Fisheries. It measures : Length, 

 81 mm. ; Height 53 mm. ; Diameter 44 mm. 



Robert E. Coker and John B. Southall, both of the U. S. 

 Bureau of Fisheries, first called attention to this shell in their 

 "Description of Shell found in the James River at Huron, S. 

 Dak., July 27, 1913," ^ in which the shell is described and fig- 

 ured, with the following statement: — "Characteristic features 

 of the shell are its triangular or pyramidal form and its remark- 

 able inflation, which are strongly suggestive of the inflated types 

 of L. luteola; its compressed sharp teeth which are of the Lamp- 

 silis type to an extreme ; the color of epidermis and character- 

 istic color of nacre, which find correspondence only in species 

 of Quadrula, especially in Quadrula undulata. The pyramidal 

 shape of the shell is also suggestive of Q. undulata. It is not 



'"Mussel resources in tributaries of the Upper Missouri River " in Rep. 

 U. S. Coramissioner of Fisheries for 1914 (1915). 



