Call — The Unionidoe of Arkansas. 6 



Lea is a young one and is by no means a fair illustration of the 

 shell. In the description of the species he mentions the 

 numerous small nodules found over its surface but the figure 

 shows the shell as smooth. The very young shells are 

 nearly as triangular as the well known Unio c/e^ans Lea. 



In 1885 the writer, without then having access to the com- 

 plete bibliography of the species, and misled by the great size 

 of the specimens submitted to him, described the form as new, 

 giving it the name of its Kansas discoverer. Later the error 

 was discovered by him and the facts fully stated.* In this 

 last named paper the remarkable character of the ctenidium 

 was made known and illustrated from specimens collected in 

 the Verdigris river, Kansas, by Mr. J. R. Mead. 



This species has thus far been only found in the Arkansas 

 and Red river drainage basins. It has not occurred to us in 

 our collecting in the State. 



Unio alatus Say. 



Nicholson's Encyc, Am. ed., Vol. IV, PI. IV, Fig. 2, 



1816. Also figured in the Am. Jour, of Science and Arts, 



Ist series, Vol. XIV, Fig. 17a and lib. Another good 



figure may be found in Conrad's Monograph of Unio, 



Plate XXXI. A figure has recently appeared, in Bull. 



U. S. Fish Commission, Vol. XIII, PI. 36, 1893, that 



is characteristic in all respects, except its alate features. 



Both ala? are broken in the specimen figured. 



This species has not been found abundantly in Arkansas. 



Its sole occurrence to us was in the St. Francis river, near 



Wittsburg, in Cross county. It has been seen by the writer 



from the Ouachita river, Indian Territory, and without doubt 



will be found in the Arkansas portion of that stream. It is 



not readily confounded with any other known Unio being, 



when perfect, easily separated from other symphynote species 



by its dark purple coloration within and its flattened disk. I 



have received it under the name of Unio purpuratus from 



which species, however, it is entirely distinct. 



From the Cedar river, Iowa, were secured very large and 



* See American Naturalist, September, Vol. xxi, 1887, p. 860. 



