ORTMANN: monograph of the naiades of PENNSYLVANIA. 



141 



This form is rather scarce in Pennsylvania. My supply of it comes chiefly 

 from a pond (old branch of Allegheny River) at Harmarville, Allegheny Co. But 

 other specimens are at hand from an artificial ice pond at Edgeworth, Allegheny 

 Co., and from a pond at Idlepark, Westmoreland Co., formed by the cutting off of 

 a part of Loyalhanna River by the railroad. Probably this form will turn up in 

 other ponds of the western part of the state. 



L. 



Size: 1. Harmarville, Cat. No. 61.4742 (c?) 149 mm. 



61.3667 ( 9 gravid) ... 148 " 



61.4742 (cf) 116 " 



do. ( 9 gravid) ... 109 " 



do. (cf) 107 " 



do. (cf) 93 " 



Comparing these measurements with those of the creek-form, given above, it 

 is clearly seen that this form stands very close to the type, but grows larger, and 

 is relatively somewhat shorter and higher. It also is distinctly thinner in the shell. 

 It is in this form, that I have best recognized the sexual differences of the shell. 



In addition there are other local forms in our region, and such are found 

 chiefly in the lakes of the glacial area in northwestern Pennsylvania. The fol- 

 lowing deserve special mention; but should not bear distinct names, since they are 

 only special reactions to special environment, and probably entirely inconstant. 



Conneaut-lake-form A. Resembles in shape and the thin shell the form 

 gigantea, but is only half as large, and the epidermis has a peculiar light green to 

 pale brown color. I have only a few specimens, which I collected on gravelly 

 bottom on the north east shore of Conneaut Lake in from three to four feet ot 

 water. 



Conneaut-lake-form B. Like form A in color (light green), but much more 

 elongated and subelliptical (not subovate). This form in shape looks almost like 

 A. marginata Say (= lacustris Lea), but traces of the beak-sculpture of grandis 

 are plainly seen. I have only a single specimen, which was collected by Mr. D. 

 Stewart, and I do not know particulars about the ecological conditions, except 

 that it comes from somewhat deeper water. L. 58 mm., H. 32 mm., D. 17 mm. 



Conneauttee-lake-form. A much elongated form, like form B of Conneaut Lake, 

 with very thin shell, but epidermis darker, green to brownish black. As in form B 

 from Conneaut Lake, the beaks appear much anterior in consequence of the posterior 

 elongation of the shell. The typical ^mnrfis-sculpture of the beaks is well developed. 



L. H. D. 

 Size: 1 115 mm. 55 mm. 39 mm. 



2 76 " 40 " 22 " 



3 50 " 25 " 15 " 



