ORTMANN: monograph of the naiades of PENNSYLVANIA. 209 



are slightlj' more compressed than the females. It is indeed often impossible to 

 ascertain the sex bj^ this character. Internally the female shell is marked by a 

 wide, oblique groove, running from the beak-cavity toward the posterior end, which 

 corresponds to the marsupium (PL XIII, fig. 2). The marsupial folds are also 

 generally marked as de]5ressions in this gi'oove. These depressions are best marked 

 in old specimens and are indistmct or absent in young ones. 



L. 

 Size: 1. Cannelton, Cat. No. 61.1166 ( 9 ) 132 mm. 



2. Harbor Bridge, Cat. No. 61.3601 (gravid 9 ) ... 125 



3. New Sheffield, Cat. No. 61.3275 (cf ) 109 



4. Shenango, Cat. No. 61.4134 (cf ) 87 



5. Rose Point, Cat. No. 61.3116 {&) 73 



6. Waterford, Cat. No. 61.4133 (9 gravid) 66 



Our largest specimens (Nos. 1 and 2) exceed the maximum size (110 mm.) 

 recorded by Scammon (1906, p. 320). 



Soft 'parts (See Ortmann, 1912, p. 306). They have been figured by Lea (Obs. 

 VII, 1860, PI. 29, fig. 101) and Lefevre & Curtis (1910, PL 1, fig. 1, and 1912, PL 6, 

 fig. 1). GlocMdia: Lea (Obs. VI, 1858, PL 5, fig. 12) poor; Ortmann (19116, PL 

 89, fig. 14). 



Breeding season: The following records for gravid females are at hand: Aug. 

 4, 1908 (eggs); Aug. 29, 1910; Sept. 1, 1908 (young glochidia); Sept. 2, 1907; 

 Sept. 6, 1908; Sept. 7, 1908; Sept. 11, 1913; Sept. 13, 1909; Sept. 13, 1915; 

 Sept. 13, 1917; Sept. 15, 1908; Sept. 15, 1915; Sept. 18, 1917; Sept. 21, 1907; 

 Sept. 21, 1908; Sept. 27, 1909; Oct. 4, 1910; Oct. 15, 1907; Oct. 15, 1908; Oct. 

 19, 1908; Oct. 21, 1908; Oct. 23, 1907. Then again: June 23, 1910 (discharging); 

 Aug. 31, 1906 (discharging). 



The beginning of the season is weU established as being the month of August, 

 and the discharge takes place in spring and early summer. Probablj^ the (single) 

 discharging individual observed on Aug. 31 was exceptionally belated. The 

 species is positively bradytidic. 



Remarks: This is an easily recognized species. The subeUiptical outline, 

 light brown epidermis, color-markmgs, and heavy hinge are unmistakable. How- 

 ever specimens of dark color and without rays might be mistaken for Elliptio 

 dilatatus, but the interior of the shell generally determines the question. 



There is a good deal of variation in shape and color. The humped shape of 

 old shells does not develop in many cases, although on the other hand it may be 

 already in evidence in comparatively small individuals. Specimens from the 

 mountain-streams (Cheat, Loyalhanna, Quemahoning) are much smaller than 



