ORTMANN: monograph of the naiades of PENNSYLVANIA. 



183 



shells are more inflated over the posterior ridge than others, and when this swelling 

 reaches considerable proportions, we may be assured that we have to deal with a 

 female. But not all females have this inflation, and often males are more inflated 

 than females of the same size. 



L. H. D. 

 Size: 1. Shenango, Cat. No. 61.4270 (cf) 96 mm. 56 mm. 35 mm. 



2. do. " " do. (9 giMvi.l) 92 " 53 " 40 



3. Rose Point, Cat. No. 61.3139 (cf) 81 " 42 " 38 



4. do. " " do. (9 gniviu).. ..73 " 39 " 27 



5. do. " " do. (cf) 68 " 39 " 28 



6. do. " " do. (9 gravid).... 63 " .36 " 26 



From the above table it is seen that the females are not always more swoUen 

 than the males. The location of the beaks is at about one-third of the length of 

 the shell from the anterior end. 



Soft 'parts (See Ortmann, 1812, p. 297). Glochidia figured by Lea (Obs. VI, 

 1858, PI. 5, fig. 27) and Surber (1912, PI. 3, fig. 42). Surber's measurements are: 

 0.35 X 0.38, while mine are: 0.33 X 0.36 mm. 



Breeding season: My records for breeding females cover the time from July 19 

 (eggs) tiU October 23. The earliest date for glochidia is September 2. It is to 



Fig. 18. 



• Alasmidonta marginata. 

 + ^4. marginala susquehannw. 



be regretted that no dates are at hand for the spring months, but the species is 

 undoubtedly bradytictic. 



