196 



Genus ARCIDOPSIS. 



Arcidopsis, Simpson, Washington, B.C., Smiths. Inst., Nat. Mus. 

 Proc. xxii, 1900, p. 861. 



TYPE, Unio footei, Theobald, from the Kistna Elver. 



The genus is represented by a single species (A. footei 

 (Theobald)). 



Original description: Shell inequilateral. elongated, with dorsal 

 and ventral lines nearly straight and parallel ; anterior end 

 strongly and obliquely truncated from the beaks to the anterior 

 base, and ending in a rather sharp but rounded point below ; 

 posterior end obliquely truncated above, rounded below ; posterior 

 ridge full, rounded ; the shell in front and below rather compressed ; 

 surface concentrically and radially ridged ; pseudocardinals strong, 

 two in the right valve, one in the left, and supported by a strong 

 cardinal rib ; muscle scars well impressed ; pallial line distinct. 



Animal unknown. 



322. Arcidopsis footei (Theobald). 



Arcidopsis footei (Theobald) ; Simpson, Washington, D.C., Smiths. 



Inst., Nat. Mus. Proc. xxii, 1900, p. 861. 

 Unio footei, Theobald, J. A. S. B. xlv, 1876, p. 187, pi. 14, 



figs. 9, 9 a. 



Original description : Testa elongata, rofcundato-quadrata, 

 valde inaequilateraii ab umbonibus angulata, et infra et antice 

 valde compressa, concentrice striata et postice radiatim striata. 

 Dentibus cardinalibus fortibus, in callo costiformi positis, in valva 

 dextra duobus alteraque singulis, subverticalibus. Cicatricibus 

 valde depressis. Pallii impressione valde conspicua. 



Hob. Kistna Eiver near the " Gutparba falls " (A. B. Foote). 



To Theobald's description is added the further note. "The 

 shell has its valves divided into two subequal areas by a strong 

 ridge running back and down from the beaks. The lower and 

 anterior portion is strongly compressed, simulating the appear- 

 ance of Area subtorta, though there is no true " version *' in the 

 valves. The strorrg cardinal rib which supports the cardinal teeth 

 is also a marked feature of this species, as well as its radiating 

 striae intersecting the concentric lines of growth. Unfortunately 

 the beaks are much decayed in my two specimens and their 

 sculpture wholly effaced." 



