482 MEMOIRS OF THE CARNEGIE MUSEUM 



Young specimens less than 30 mm. long have not been found in spring, with 

 one exception, when a female of 25.5 mm. in length was found on May 27, 1904, at 

 Squaw Run. This, however, apparently was an exceptionally delayed individual 

 of the generation of the previous year. It was found under unusual conditions, 

 under a stone on the banks of the creek, evidently removed from its original habi- 

 tation by winter or spring floods. No additional specimens were seen in close 

 proximity. 



I cannot say much in the case of C. diogenes in reference to the regular moult- 

 ing periods which were observed in C. obscunis to take place in spring and fall. I 

 have repeatedly found soft shells, and on April 24, 1904 (Nine-Mile Run, Pitt>-'- 

 burgh). at a place where a large colony of this species was present, I picked up 

 numerous cast-off claws,™ which would indicate an early spring moult. But these 

 claws may have accumulated during winter and spring. The rate of increase at a 

 moult was measured in one instance. A female, 52 mm. long, captured on April 

 6, 1905, was kept in captivity, and moulted on July 16. After this process it was 

 54 mm. long. This cannot be regarded as entirely normal, since the specimen was 

 kept under unfevorable and artificial conditions. 



The copulating season of this species also falls in the autumn. I have only 

 twice observed a male and female in copulating attitude, but in both cases they let 

 go when disturbed. This was on November 5, 1904 (Nine-mile Run, Pittsburgh), 

 and on October 24, 1905 (Branchton, Butler County). The first couple was found 

 in water inside and near the mouth of a comparatively simple hole. The male was 

 70 mm., the female 81 mm. long. The second couple was found a little deeper, but 

 not over a foot, also in water. The male was 61 mm., the female 03 mm. long- 

 IMr. F. E. Kelly reports a similar observation made by him on November 14, 1904. 

 Besides on two other occasions I found males and females associated in couples in 

 the same hole. Three cases were observed on September 5, 1904, at Sniithfield, 

 Fayette County, and two cases on August 26, 1905, at Baden, Beaver County. 

 Since it is an absolute rule that under ordinary circumstances only one specimen 

 occupies a hole, these finds are .significant, and, inasmuch as in all these cases it 

 was always a male of the first form which was associated with a female of good size 

 (over 63 mm. long), it is evident that this association was connected with the mating 

 process. Whether the male visits the female, or vice versa, 1 do not know. In 

 every case the pair was easily captured, being lodged not far from the entrance of 

 the hole. In some of these cases I was struck by the simple character and small 

 depth of the barrow, and it may be that the couples dig out small, temporary holes 



'j After moulting the shell is generally eateu up, with the exception of the bit; claws. 



