20 Trans. Acad. Sci. of St. Louis. 



the types. It was collected by Dr. Byrd Powell, near Hot 

 Springs, Arkansas, and was described from two unmatched 

 valves belonging to old individuals. Keeve gives a very good 

 figure, probably copied from Lea, but is hopelessly confused 

 on the relations of the form. He does not recognize the name 

 of Lea, save as a synonym, but places it under Unio 

 nodulosus Wood. He suggests that it has an aspect very 

 much like that exhibited by certain Chinese shells, and 

 thinks that both <* may prove to be the Chama plumbea 

 of Chemnitz." It is hardly necessary to say that there is no 

 relation to Chama, and no question but that the shell is prop- 

 erly credited to Arkansas. It is a member of the pustulate 

 group and is not far removed from Unio cooperianus^ which it 

 closely resembles. 



Unio irroratus Lea. 



Trans. Am. Philos. Soc, Vol. Ill, 1827, p. 269, PI. 



V, Fig 5. Described from Ohio. 



Unio irroratus Lea, Eeeve, in Conch ologia Iconica, 



Unio PI. XII, Fig. 44, female. 1868. 



Unio stegarius Rafinesque, so Conrad, in Monograph 



of Unio, p. 83, PL XL VI, Fig. 1, 1838. Also Reeve, in 



Conchologia Iconica, Unio Plate XII, Fig. 45, male. 



1868. 

 This species occurred in the St. Francis river, at Witts- 

 burg, and in the Saline, at Benton. In the first mentioned 

 locality it is very abundant and specimens of all ages were 

 found. The very young have the outline of Unio elegans,h\xt 

 they are somewhat longer than the young of that species at a 

 corresponding age. The resemblance of very many of the 

 young to the form described by Conrad as Unio aherti is also 

 marked. The triangular outline is lost with age, and the cir- 

 cular form becomes more and more marked. Closely allied 

 to it is the common Unio dromas Lea, of the Cumberland 

 river. 



Unio hydianus Lea. 



Trans. Am. Philos. Soc, 2nd series. Vol. VI, 1834, p. 

 14, PI. VI, Fig. 14. 

 This species was described from the Bayou Teche, Louis- 



