134 MEMOIRS OF THE CARNEGIE MUSEUM. 



L.. H. D. 



Size: 1. Conneaut Outlet, Cat. No. 61.3315 (cf ) 124 mm. 93 mm. 40 mm. 



2. Waterford, Cat. No. 61.4238 (d') 118 " 86 " 40 " 



3. do. " " do. (9) 118 " 84 " 39 " 



4. Conneaut Outlet, Cat. No. 61.3315 ( 9 ) H" " 88 " 35 " 



5. do. " " do. (9) 93 " 71 " 23 " 



6. Waterford, Cat. No. 61.4237 (c?) 90 " 65 



2 



o 



do. Cat. No. 61.4238 (c?) 78 " 60 " 21 



a 



Outside of Pennsj'lvania this species grows much larger. 



Soft parts: Figured by Lefevre & Curtis, 1910, PL 1, fig. 6, and 1912, PI. 6, 

 fig. 3; described by Ortraann, 1912, p. 282. Glochidia (See Lea, Obs. VI, 1858, 

 PI. 5, fig. 29; Lefevre & Curtis, 1910, p. 97, fig. A, and 1912, p. 146, fig. A; Ort- 

 mann, 19116, PI. 89, fig. 11; Surber, 1912, PL 1, fig. 6. Lefevre & Curtis give the 

 dimensions: 0.28 X 0.30 mm.; Surber: 0.310 X 0.320; while I gave: 0.34 X 

 0.34 mm. 



Breeding season: I found gravid females on September 14, 1909; September 

 22, 1910; and May 14, 1908. Glochidia were observed on the first and last dates. 

 Although these records are very meager, yet they distinctly indicate that we have 

 to deal with a bradytictic form, which carries the glochidia over winter. According 

 to Surber (1912, p. 7), this species is gravid in October, November, and May. 



Remarks: An extremely characteristic species, which in its external shape 

 greatly resembles Proptera alata (Say), but may be distinguished at once by the 

 color of the nacre (white, not purple), by the hinge, and some minor characters. 

 The similarity of the outer shape of these two species, belonging to different sub- 

 families, is very remarkable, and offers a very good example of parallel, but inde- 

 pendent, development of the same external characters ("convergency"). 



Aside from slight differences in outline and the variability of the hinge, this 

 species varies chiefly in the development of the sculpture of the posterior slope. 

 In Pennsylvania both conditions, specimens with well-developed sculpture, and 

 with practically smooth shells, are found side by side, accompanied by all tran- 

 sitional stages. In size the Pennsylvanian shells remain far below the dimensions 

 recorded for specimens from farther west (Scammon gives: L. 188; H. 110; D. 

 52 mm.). 



Localities in Pennsylvania represented in the Carnegie Museum: 



Conneaut Outlet, Conneautlake, Crawford Co. 

 Leboeuf Creek, Waterford, Erie Co. 



Other localities represented in the Carnegie Museum: 



Lake-drainage : 

 St. Josephs River, Fort Wayne, Allen Co., Indiana (C. Goodrich). 



