CaU — The Unionidm of Arkayisas. 37 



series, Vol. VI, 1868, PI. 48, Fig. 122, p. 309. Based 

 upon a young specimen from the Brazos river, Texas. 



Unio UncecumuLtea. Jour. Acad. Nat. Sci. Phila., 2d 

 series, Vol. VI, 1868, p. 312, PI. 49, Fig. 125. Species 

 based upon three specimens from the Brazos river, 

 Texas . 



Unio perplicatus Conrad. Jour. Acad. Nat. Sci., 

 Phila., 2d series. Vol. VIII, p. 178. 



Unio pauciplicatus Lea. Jour. Phila. Acad. Nat. Sci., 

 2d series, Vol. VIII, 1874, p. 29, PI. 9, Fig. 26. De- 

 scribed from specimens obtained in the Colorado river, 

 Austin, Texas. 

 Reeve also figures, under the MS name of Unio perlensis 

 Conrad, with the habitat ♦» North America ", a shell contributed 

 to the Museum Cuming by John G. Anthony, which appears to 

 be an abnormal form of this species. Vide Conchologia 

 Icouica, Vol. XVI, Unio Plate XI, Fig. 42. 



This Unio occurs in great numbers in the St. Francis river, 

 at Wittsburg, rivaling all others, save, perhaps, Unio trape- 

 zoides Lea. The form is the short and somewhat ventricose 

 one, which Mr. Conrad called perplicatus. It also occurred in 

 some abundance in the Saline river, at Benton. 



The form which Mr. Lea called Unio hippopceuSy from 

 Lake Erie, is without question a depauperate plicattts and is 

 not entitled even to varietal distinction. Throughout the great 

 geographical range of this species almost every possible variety 

 of environment is to be found, and it would be strange indeed 

 if the shells did not in some measure respond to these factors. 

 It is usually abundant, wherever it occurs at all. In central 

 Iowa it is rare, but in the Mississippi river, on the eastern border 

 of that State, it is both common and large. In the Cumber- 

 land river it is a very abundant shell; and is, in short, to be 

 reckoned among the most common of our Uuios. In Ar- 

 kansas, aside from the localities named above, the shell is said 

 to be abundant in the Little Red river, though we have not 

 seen specimens that came from that stream. From the Cedar 

 river, Iowa, was obtained a specimen which presented the 

 following dimensions: length, 135 mm.; height, 98 mm.; 

 breadth, 59 mm. 



