ORTMANN: monograph of the naiades of PENNSYLVANIA. 131 



In the drainage of the Great Lakes, from Wisconsin through Michigan to New 

 York and eastern Canada it is widely distributed. However this latter part of 

 its range shoukl be investigated more closely. As we shall presently see, in Lake 

 Erie a peculiar local variety has been developed. Nevertheless in the lake-drainage 

 in western and central New York the normal type is present. Here it advances 

 along the Erie Canal to the Mohawk and even to the Hudson River. It follows 

 the lower St. Lawrence down to the neighborhood of Ottawa and Montreal (and 

 also occurs in the Lake Champlain region), but it is not known whether the form 

 peculiar to Lake Erie or the normal type prevails here. 



It should be further noted that the rule that this species is rare in large rivers 

 holds good also in the Ohio below Pittsburgh. Between the Pennsylvania state- 

 line and. Cincinnati, I found only a single individual (in a clam-digger's pile at 

 Portsmouth, Scioto Co., Ohio). This is in strong contrast to the abundance of 

 this species in some of the smaller creeks in West Virginia and Kentucky. 



Lasmigona (Lasmigona) costata eriganensis Grier (1918). 



A form, not distinguished hitherto, except by Sterki (1907a, p. 393) who called attention to its 

 peculiarities, and by Grier (1918, p. 10) who elevated it to the rank of a variety. 



Plate IX, fig. 6. 

 Characters of the variety: Shell smaller, slightly more elongate, more swollen, 

 and thus approaching in a degree the subcj'lindrical shape. Ridges of posterior 

 slope generally narrower. Color lighter, more yellowish-brown, sometimes rusty 

 brown, with the rays indistinct, and the growth-rests more distinct and more 

 regular. 



L. H. D. 



Size: 1. Presque Isle Bay, Cat. No. 61.4223 . . .90 mm. 44 mm. 31 mm. Type Set 



2. do. do. ...88 " 45 " 26 " " " 



3. do. do. ...85 " 46 " 29 " " " 



4. do. do. ...76 " 39 " 28 " " " 



5. do. do. ...73 " 38 " 25 " " " 



Compared with the measurements of typical costata (p. 126), the differences 

 in shape become evident, especially the greater diameter. 



Soft parts: Living specimens have been found only on two occasions: May 22, 

 1909; and July 8, 1910. Although there were females among them, none were 

 gravid. The soft parts of none were preserved, but as far as I am able to recol- 

 lect, they were not different from the normal form. 



Remarks: Although I have only fifteen specimens from Pennsylvania, and 

 five from JNIichigan (to which might be added aboiit half a dozen individuals used 



