Call — The Unionidce of Arkansas, 19 



near the margin, and on gravelly bars ; it also occurs commonly 

 in muddy stations having the habit of Unio parvus Barnes 

 which heads the group of which Unio glans is a member. 

 Unio ellipsiformis^ Conrad (Monograph of Unio Plate 34, Fig. 

 1, p. 60), 1838, described from Michigan, is also a synonym. 



Unio gracilis Barnes. 



Described in the Am. Jour. Sci. and Arts, Ist series, 

 Vol. VI, 1823. 



Unio fragilis Eafinesque, so Conrad, in Monograph of 

 Unio, Plate XXX, 1836. 



Unio dolosus Lea. 1860. Jour. Acad. Nat. Sci. 

 Phila., Vol. V, 1861, p. 75, PI. IX, Fig. 224. Also Con- 

 chologia Iconica, Reeve, Unio Plate XLI, Fig. 228. 

 This is a poor figure of an immature specimen. 



Unio gracilis Barnes. Reeve, Conchologia Iconica, 



1868, Unio Plate XXXIX, Fig. 215. This is a figure of 



an old specimen but does not show the characteristic 



alation of the dorsal margin. 



This species has occurred to us in the Saline river, at Benton, 



and in the St. Francis river, at Wittsburg. It does not differ 



in any material respect from the forms found so abundantly 



in the sloughs along the Mississippi river farther to the north, 



and in all the larger streams which are tributary to it, except, 



perhaps, the Missouri river alone. Lea's dolosus is very 



abundant in the Coosa river at Wetumpka, and in the Alabama 



at Selma. It was also found in numbers in the Cahaba, at 



Lily Shoals, in Bibb county. There can be no doubt of its 



identity with the older form described by Barnes. 



The typical form of the group that it heads, this species 

 ranges from the Ottawa river, Canada, to Minnesota, Iowa, 

 and Kansas, and south to Central Alabama and to Texas. 



Unio grandidens Lea. 



Jour. Acad. Nat. Sci. Phila., 2d series, 1862, Vol. V, p. 



205, PI. XXX, Fig. 274. Also Reeve, in Conchologia 



Iconica, 1868, Unio Plate LXXXIII, Fig. 439. 



This species has not been found by us in Arkansas nor do 



we know of the existence of any specimens other than 



