30 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 123 



abdomen is flexed; central projection spiculiform and both it and 

 mesial process straight, the former slightly curved caudally near tip; 

 cephalic surface of shaft with prominent shoulder just proximal to 

 base of central projection. Annulus ventralis with transversely oval 

 depression extending cephalically beneath cephalic wall, latter 

 bearing median cleft. 



Range. — From Ohio and Kentucky southward to northwest 

 Georgia west of the Alleghenies, and in the headwaters of the James 

 River in Craig County, Va. 



Specimens examined. — 300 specimens in 22 collections from 

 stations 7 and 42. The occurrence of 0. juvenilis in the Mountain 

 Lake area represents two probable introductions (see p. 10 and 

 below), and that at station 7 is the first record of the presence of 

 this species on eastern slopes of the Allegheny Mountains. These 

 stations are located at elevations of 671 and 1180 m respectively. 



After this manuscript had been completed, two specimens of 0. 

 juvenilis were found in the New River, 500 m south of the mouth of 

 Spruce Run in the vicinity of a fishing camp. 



Associates. — At station 7, 0. juvenilis was found with C. b. bartonii 

 and C. I. longulus; in Mountain Lake (sta. 42) it is not accompanied 

 by any other crayfish at the present time. 



In station 42, neither ostracods nor branchiobdellids infest the 

 members of this population. At station 7, the ostracod associates 

 include Dn. ileata, Dn. scalis, and P. phyma; the branchiobdellid 

 associates, C. holostoma and Xg. instabilius. 



Remarks. — With regard to the population of 0. juvenilis in 

 Mountain Lake (see Hobbs and Walton, 1966a), it is perhaps of 

 interest that in 1933 C. b. bartonii was the only crayfish inhabiting it. 

 The latter was, and is still, the only crayfish in the small stream, 

 "Pond Drain," flowing from the Lake. In 1933, members of one of 

 the classes in aquatic biology at the Biological Station brought 

 collections of animals from the vicinities of their homes and released 

 them in the Lake. In 1947, three species were found to be present 

 and with few exceptions were restricted to different regions of the 

 Lake. Orconectes juvenilis occurred along the east and to a lesser 

 degree along the south side; C. acuminatus, never observed by us to 

 be abundant, was found only along the north side and never closer 

 than 100 yards from the outlet; C. b. bartonii was found in the area 

 of the outlet, at the northwest corner. According to our observations, 

 crayfishes have never been abundant along the west side (perhaps 

 they are inaccessible because of the greater depth of the water), and 

 we have no records of what species, if any, frequent this area. By 

 1954, there were no C. acuminatus to be found in any of the littoral 

 areas, and it seemed that 0. juvenilis was invading the north side; 



