2 THE NAUTILUS. 



tion of a river forming a barrier to aquatic animals." It 

 may be of interest to recite similar instances as they apply to 

 Goniobasis. 



Say's G. semicarinata lives in streams upon both sides of 

 the Ohio river. It does not, I am convinced, inhabit the river 

 itself. Shells that one may identify as semicarinata have 

 been sent out from Cincinnati, and it has been assumed that 

 the material came from the Ohio. The collection of the Uni- 

 versity of Cincinnati leads me to believe that the shells were 

 taken, not in the Ohio, but in the Little Miami river and in 

 Mill creek, close at hand. A barrier is plainly indicated by 

 the difference in the species on the two sides, the semicarinata 

 of the Kentucky streams being smaller, darker, the carinae 

 less pronounced, than in Ohio and Indiana streams. 



In the Blue river of southern Indiana, Daniels found a 

 Goniobasis that Pilsbry described under the name indianensis. 

 So far as the records show, the race is confined to that stream. 

 In Hardin county, 111., the streams of which are tributary to 

 the Ohio, occurs a plicate Goniobasis which is identified as 

 costifera Hald. In Pigeon creek at Evansville, Ind., I found 

 a species of the genus which, if not new, is exceedingly rare 

 in collections. It has no counterpart in streams explored else- 

 where in Indiana and in Ohio and, so far as I know, in Ken- 

 tucky and Illinois. To the list of isolated races of the region 

 can be added G. eliminata Anth. In all these instances, the 

 Ohio river has acted as a barrier, preventing the interbreed- 

 ing of the races of one species, permitting the development of 

 small, distinct races, acting as a wall between the inter- 

 distribution of the Goniobases of the Licking, Kentucky and 

 Salt rivers on one part and of the Green river Goniobases on 

 another. 



Goniobasis depygis Say is recorded as from the Falls of the 

 Ohio. I have collected there three times and never found 

 specimens of the genus. None appears in the Daniels collec- 

 tion, and in a large sending from this locality to Dr. Bryant 

 Walker, from Billups, there were no Goniobases. My own 

 suspicion is that depygis is a Lithasia as surely as is the G. 

 louisvillensis of Lea. 



