Nos. IAND2.] COTYLASPIS INSIGNIS. 7 



occurrence of Cotylaspis, as well as of Aspidogasfcr, is more con- 

 siderable in those places, the supposition is aroused that possibly 

 the distribution of the parasite has been from the lower to the 

 higher parts of the river system and that its absence from the 

 other Unionidae in Chautauqua Lake means a shorter period 

 since its introduction there. His figures indicate a preference for 

 Anodonta, and if, for any reason, the numbers of Cotylaspis in the 

 lake are limited to the number that can be accommodated by the 

 Anodonta population, then we should not expect to find them out- 

 side of that form. The idea of a comparatively recent arrival of 

 the flukes in Lake Chautauqua would harmonize with this inter- 

 pretation of the distribution. Kelley's list of localities includes, 

 besides the Schuylkill system and the Mississippi system, the 

 Susquehanna River system as included in the distribution of 

 Cotylaspis. It will be interesting to find .whether it occurs in 

 other rivers of this country. It appears probable that it is much 

 more common in this country than in other parts of the world. 



A summary of these facts includes the following points : 



Cotylaspis is confined to Anodonta and not found in Unio. 



It is nearly universally present in Anodonta. 



Its numbers are not in direct relation with the size and age of 

 Anodonta. 



Its numbers vary directly with the purity or impurity of the 

 water in which the host is found. 



c. Habits. 

 Cotylaspis is most commonly found firmly adhering by its large 

 ventral sucker to the free outer surface of the kidney of its host 

 (see Fig. i). It is also, but less often, found adhering to the 

 free edge of the inner gill plate or to the adjoining surfaces of the 

 visceral mass. By opening the mantle chamber of the mussel and 

 pushing the gills aside, the kidney is displayed and the fluke can 

 be seen in its natural position. Its body presents two distinct por- 

 tions, the large oval adhesive " ventral sucker," arising from 

 which and extending obliquely upward and forward is the slender 

 and extremely mobile body of the animal. In life the body is 

 kept swaying, first to one side and then to the other, and its 

 dilated tip touched to the kidney surface. By watching it with 

 a lens the following events are seen to take place : First there is 



