4 OSBORN. [Vol. XVIII. 



to two miles, with wooded or open sloping shores. It is situated 

 at the head of a small river which finds its .way into the Alle- 

 gheny at Warren, Pennsylvania, and thus belongs to the Missis- 

 sippi River system. There are a number of summer resorts on 

 the lake, and the greatest among them. The Chautauqua Assembly, 

 has a permanent summer population of perhaps fifteen thousand 

 people, which is occasionally swelled for the day to perhaps twice 

 that number. At the foot of the lake the city of Jamestown is 

 located. A complete exploration of the lake has not been possible, 

 but collections have been made at localities in different parts, in- 

 cluding both ends and the middle of the lake, and where the bot- 

 tom was different as clean and sandy, shelly and stony with weeds, 

 and muddy, but only on or near the shore .where material could 

 be taken from a boat or by wading. Several different species of 

 Unionidje are found in all of these situations. Off the Assembly 

 grounds, which are located three miles from the head of the lake, 

 we find Anodonta plana Lea and less often A. grandis. Unio 

 luteolus Lam. is the commonest species of Unio, while U. edcntu- 

 lus Say is very common, and U. ventricosits, U. phaseohis Hild. 

 and U. gihhosns Bar. are found more rarely. I have examined a 

 great many individuals of all of these forms during the seasons 

 of '95, '96, '97 and '98, chiefly from the shore at Chautauqua 

 Assembly, and as a general result can say that Cotylaspis occurs 

 in all parts of the lake and that it is almost totally confined to 

 Anodonta, being found in Unio only in two instances (in U. 

 luteolus). For the sake of a record I will state here that my 

 specimens were obtained at the following points on the lake : 

 near the head of the lake at Point Chautauqua and Chautauqua 

 Assembly; in the middle of the lake at Long Point and Bemus 

 Point, and at the foot of the lake at Celoron. I also collected at 

 the beginning of the " outlet," and at the river at Jamestown. 



The preference of the fluke for Anodonta is surprising, since 

 U. luteolus is equally abundant and U. cdentulus also is very fre- 

 quent. At one time I thought that it might be attributed to the 

 fact that in Anodonta the kidney is directly accessible from the 

 branchial chamber, .while in Unio luteolus it is not, owing to the 

 fact that the inner gills coalesce with the adjacent surface of the 

 visceral mass. But the same communication as in Anodonta ex- 



