THE NAUTILUS. 99 



THE BREEDING SEASON OF UNIONID.E IN PENNSYLVANIA. 



BY DR. A. E. ORTMANN. 



(Concluded from page 95.) 



Symphynota viridis Conr. August 24, '08, four gravid females 

 were found among a dozen specimens ; of 35 specimens collected by 

 Dr. D. A. Atkinson on July 11, '08, not a single one was gravid. 



Symphynota costata Eaf. Autumn (Lea, III, '42); March, Oc- 

 tober (Lea, ibid.'). I found gravid specimens in April, May (latest 

 date, May 26), and then again in August (earliest date, August 9), 

 September, October. Numerous specimens were collected in June 

 and July, but none of them was gravid. 



Symphynota complunata Barn. Autumn (Lea, III, '42) ; March 

 (Lea, ibid.). Gravid females found on May 14, '08. 



Alasmidonta undulata Say. September und October (Lea, II, 

 '38). Gravid females on July 18 and August 12. 



Alasmidonta heterodon Lea. August, September (Lea, II, '38); 

 May (Lea, X, '63). 



Alasmidonta marginata Say. October and December (Lea, II, 

 '38). The western form was found gravid in August, September, 

 October. Out of a number of specimens collected on June 5, 8 and 

 22 none was gravid. No dates at hand for July. The eastern form 

 was found gravid on August 13. The western form (= truncata 

 Wright = typical marginata Say) is hardly distinguishable from the 

 eastern (=var. varicosa Lam.), see Pilsbry and Fox, NAUTILUS, 

 '01, pp. 16 and 17). 



GROUP B. SUMMER BREEDERS. 



Some of the summer breeders ( Unio, Pleurobema) have the outer 

 gills only serving as inarsupium, in others (^Quadrula) all four gills 

 are supposed to assume this function in the breeding season. Yet in 

 many Quadrulas this condition is unknown, and, as we shall see be- 

 low, the arrangement of the species into genera will need revision 

 and correction. I enumerate the species here according to Simpson's 

 Synopsis. 



Unio gibbosus Barn. Summer breeder (Sterki, '95); July, Aug- 

 ust (Lea, III, '42). I found gravid females of this common species 

 in June and July, and a single belated one on August 13. Hun- 



