ORTMANN: monograph of the naiades of PENNSYLVANIA. 291 



in different localities. A specimen from Nipigon Straits is absolutely like the 

 Lake Erie form, while others from Six Mile Lake (a shallow lake on Thundercape 

 Peninsula) have irregular growth-lines, and incline more toward normal luteola. 

 These specimens could not very well be called superiorensis, for they do not have 

 a dark epidermis. Then again specimens from Kaministiquia River (tributary 

 to Lake Superior at Fort William) are darker in color, and might possibly represent 

 the real superiorensis. 



Specimens from Sheyenne River,- North Dakota, are indistinguishable from 

 certain Lake Erie specimens, except for the irregular growth-lines. 



I have the impression that rosacea is not so much a geographical, as an eco- 

 logical race, produced by the en\'ironment of great lakes, and that it turns up, 

 whenever the proper conditions are offered. Since this environment is very widely 

 distributed in the northern states and in Canada, rosacea appears as a geographical 

 race. In this connection it should be emphasized that this variety is not found 

 in the tributaries of the lakes, but that the normal fonn of luteola exists there. 

 There are also certain lakes, in which the form rosacea is not present, for instance 

 Lake Chautauqua, and Conneaut Lake. In the latter luteola is quite typical. 



More detailed investigations are required to finally determine this question. 

 It also should be ascertained to what factors the rose-colored nacre may be due. 

 Our specimens from Sandy Lake, Ontario, have red nacre, and come from a lake, 

 the water of which is, according to Mr. G. H. Clapp, heavily charged with lime. 



Localities in Pennsylvania represented in the Carnegie Museum: 



Lake Erie, Presque Isle Bay, outer shore, and beach-pools of Presque Isle, Erie, Erie Co. 



Other localities represented in the Carnegie Museum: 



Lake Ontario, Braddock Bay, Manitou Beach, Monroe Co., New York (R. H. Santens). 



Lake Erie, Sandusky Bay, Cedar Point, Erie Co., Ohio (C. Brookover) (0. E. Jennings); La Plaisance 

 Bay, Monroe Co., Michigan (C. Goodrich); Crystal Beach (F. Behrle) and Port Colborn, Welland 

 Co. (C. Goodrich); Port Rowan and Port Dover, Norfolk Co., Ontario, Canada (C. Goodrich). 



Sandy Lake, Peterboro Co., Ontario, Canada (G. H. Clapp). 



Grand River, Cayuga, Haldimand Co., Ontario, Canada (C. Goodrich).''" 



Winona Lake, Kosciusko Co., Indiana (E. B. Williamson) (not typical). 



Lake Wiwassee, Kosciusko Co., Indiana (C. Goodrich). 



Lake Huron, Port Huron, St. Clair Co., Michigan (N. M. Grier); Saginaw Bay, Michigan (Smith col- 

 lection). 



Big and Little Whitefish Lakes, Pierson, Montcalm Co., Michigan (Miss M. O'Malley). 



Au Sauble Lakes, Lake Co., Michigan (C. Goodrich). 



Douglas Lake, Cheboygan Co., Michigan (H. B. Baker). 



"" A small race of luteola, and probably var. rosacea, although not typical. It should be noted 

 that in the Upper Grand River-drainage (Conestogo River), the real L. luteola is present. 



