ORTMANN: monograph of the naiades of PENNSYLVANIA. 163 



with dark green, more or less distinct, rays on the whole disk. Two or three dark 

 green to blackish rays generally well developed upon the posterior slope. 



Hinge edentulous, forming a straight line, or with a faint indication of a wave 

 under the beaks. Beak-cavity shallow. Dorsal muscle-scars in the beak-cavity. 

 Adductor muscle-scars indistinct. Nacre blueish white, silvery, iridescent, some- 

 times shghtly cream-color toward the beak-cavities. 



This species being a hermaphrodite does not show any sexual differences in 

 the shell. 



L. H. D. 



Size: 1. Erie, Cat. No. 61.3291 83 mm. 41 mm. 28 mm. 



2. Waterford, Cat. No. 61.4178 ....'. 67 " 32 " 24 " 



3. do. " " do .56 " 27 " 16 " 



4. Edinboro, Cat. No. 61.3290 48 " 2.5 " 12 " 



The largest specimen represents about the maximum size attained by this 

 species. Generally it remains considerably smaller (Length between 50 and 

 60 mm.). 



Soft parts (See Ortmann, 1912, p. 291). Glochidia figured by Lea (Obs. VI, 

 1858, PI. 5, fig. 36); Ortmann (1911, PI. 89, fig. 13); Surber (1912, PI. 1, fig. 2). 

 Surber's measurements are: 0.31 X 0.29 (longer than high), while I gave: 0.30 X 

 0.31 mm. (higher than long). 



Breeding-season: My dates for gravid females are: June 2, 1908 (eggs); 

 July 12, 1910 (discharging); Sept. 14, 1909 (eggs and glochidia); May 21, 1908 

 (glochidia and discharging); May 22, 1909 (glochidia and discharging); May 

 24, 1909. Surber (1912, p. 7) gives March, June, July, August, and September as 

 months when gravid individuals are present. From Arkansas I have gravid 

 specimens collected by Wheeler on February 20, 1913; June 14, 1911; July 17, 

 1911; and in November, 1911. 



This is undoubtedly a bradytictic form, and according to the above dates, it 

 apparently breeds "all the year round," i.e., the succeeding breeding seasons 

 overlap in June and July, but probably not in the same individual. 



Remarks: A well-marked species, which is easily recognized by its shape and 

 color. As far as my material permits a conclusion, it varies very little, and the 

 variations are restricted to the proportional length of the shell and its degree of 

 obesity; the latter of which in part depends on age. The color of the epidermis 

 is also somewhat variable, being lighter or darker green, but specimens from the 

 same localitj^ are generally very uniform. 



Localities in Pennsylvania represented in the Carnegie Museum: 



Lake Erie, Presque Isle Bay, Horseshoe Pond, and beach-pools on Presquc Isle, Erie, Erie Co. 

 Leboeuf Creek (outlet of lake), Waterford, Erie Co. 



