110 THE NAUTILUS. 



This is a striking contrast to the fii*ni, pebbly bottom of Dorcheat. 

 My collecting was done near Port Bolivar in Bienville Parish. 



Before the railroad was built from Shreveport to Monroe, in high 

 water steamboats ascended Lake Bisteneau and Dorcheat Bayou to 

 the steamboat landing two miles from Minden, in Webster Parish. 



This stream, Dorcheat and Bistenean really being one stream, is of 

 considerable interest on account of its shells. Of these it has a fair 

 number of species. There are some interesting facts presented as 

 regards the differences in the mollusks of the different portions of 

 this same stream ; for instance : I could not find a single specimen of 

 Unio hydianus, castaneus, nigerrlmus or turgidus in the portion of 

 Bistenean that I examined, Avhile all are \evy abundant in Dorcheat. 



The specimens of castaneus were nearly all much thickened ante- 

 riorly, something that was not noticed in specimens of castaneus col- 

 lected elsewhere. The nlgerrimus were larger and thicker shells 

 than any other specimens found here. The specimens of nigerrhmis, 

 hydianus, castaneus and anodontoides, in Dorcheat, were found usu- 

 ally where they had bored into the sloping banks, about at the 

 tuater's edge. The other specimens of Unio were found mostly on the 

 rocky bottom. I have only one mississippiensis from Dorcheat. It 

 was given me in a large lot of shells from there. 



The anodontoides from Lake Bistenean were large, heavy shells. 

 It was the most abundant species of Unionidce there. The bottom 

 of Bistenean in many places was almost covered with Campeloma 

 decisa, and Vivipara suhpurjnirea. Avinicola cincinnatiensis was 

 very abundant. 



The following is a list of the species with their localities. 



Unio anodontoides Lea. Bisterneau, Dorcheat. 



Unio boykinianus Lea. Dorcheat. 



Unio castaneus Lea. Dorcheat. 



Unio chunii Lea. Dorcheat. 



Unio gracilis Bar. Bistenean, Dorcheat. 



Unio houstonensis Lea. Bistenean. 



Unio hydianus Lea. Dorcheat. 



Unio lachrymosus Lea. Bistenean, Dorcheat. 



Unio mississippiensis Con. Dorcheat. 



Unio mnltiplicatus Lea. Dorcheat. 



Unio nigerrinius Lea. Dorcheat. 



Unio purpuratus Lam. Bistenean, Dorcheat. 



