Call — The Unionidce of Arkansas. 33 



Unio occidentalis Conrad. 



Monograph of Unio, 1836, p. 64, PI. XXXVI, Fig. 1. 



This is an abundant species in central Arkansas, particularly 

 in the Little Red river. Van Buren county ; found also in the 

 White river, Carroll county; Saline river, Benton, Saline 

 county. 



There is no other form with which this species will be easily 

 confused. It groups with Unio phaseolus Hildreth, but is quite 

 distinct from that form; it is commonly much smaller. It 

 was described originally from the Current river, Arkansas, 

 and is not yet known to occur outside of the State. 



Unio ozarkensis Call. 



Plate XVIII. 



Proc. U. S. Nat'l Mus., Vol. X, p, 498, PI. XXVII, 1887. 

 The original description of this species follows: — 

 Shell smooth, elliptical, somewhat compressed laterally, 

 inequilateral, thick, but thickest anteriorly; epidermis thin, 

 striate toward the margins, yellowish-brown, or olivaceous, 

 marked with numerous, obscure, narrow, green rays disposed 

 regularly over the central portion of the disk ; lines of growth 

 rather numerous, dark, well marked ; dorso-posterior margin 

 curved; posterior umbonal slopes always eradiate, more or 

 less biangulate, which angulations continued posteriorly mark 

 the siphonal area and render the posterior margin bianguiar; 

 umbones small, triangular, scarcely prominent, approximating, 

 marked — in non-eroded specimens — by two or three rather 

 coarse undulations; ligament short, thick, light brown; car- 

 dinal teeth disposed to be double in both valves, short, oblique, 

 thick, unequally bifid, striated, the posterior division generally 

 thickest and heaviest; lateral teeth rather short, slender, 

 slightly curved, crenulate at extremities, in general direction 

 forming nearly a right angle with a line drawn through the tip 

 of the umbo and the anterior division of the cardinal tooth ; 

 anterior cicatrices deep, pit-like, striate, confluent, though in 

 occasional specimens the protractor-pedis impression is distinct 

 from the adductors and deep; posterior cicatrices distinct, 

 that of the adductor muscle being usually well impressed, that 



