64 



PROCEEDINGS OF THE NATIONAL MUSEUM 



Xironogiton instabilius (Moore) 



Figures 22a-d 

 Branchiobdella instabilia Moore, 1894, p. 425. 

 Bdellodrilus instabilius Pierantoni, 1912, p. 22. 

 Xironogiton instabilius Ellis, 1919, p. 252. 

 Xironogiton instabilius instabilius Goodnight, 1940, p. 45. 



Diagnosis. — Dental formula 5/5 or 4/4, teeth irregular in shape 

 with some median teeth shorter than lateral ones on both jaws. 



Range. — Swift, colder streams of the mountains from Ontario to 

 Georgia; a form at present indistinguishable from Xg. instabilius is 

 the most common branchiobdellid in the streams of the western 

 slopes of the Sierra Nevada and Cascade Mountains of California, 

 Oregon, and Washington west to the Pacific Ocean. 



Specimens examined. — More than 100 specimens in 24 collections 

 from the following stations: 3-5, 7, 9, 11-13, 21, 22, 24, 37, 44, 46, 53, 



# 



C 



d 



Figure 22. — Xironogiton instabilius: a, dorsal view of entire animal; b, ventral view of burs£ 

 and spermiducal gland; c, upper jaw; d, lower jaw. 



54, 60, 61, 64, 86, 95, 97, 121, and 123. These stations are in the 

 headwaters or swifter tributaries of the James and New river drainages 

 at elevations of 512 to 1097 m. 



Hosts and associates. — Xironogiton instabilius was associated 

 with Cambarus b. bartonii at all stations except 11, 13, 61, 86; with C. 

 carolinus at 22; with C. I. longulus at 7, 9, 11, 12, 13, 21, 22, 37, 123; 

 with C. sciotensis at 3, 5, 44, 54, 61, 64, 86, 95, 97; and with 0. juvenilis 

 at 7. 



Ostracod associates includes As. asceta and Dt. chalaza at station 22 ; 

 Dn. ardis at 11-13, 21, 37, 123; Dn. ileata at all stations except 13, 53, 

 121; Dn. scalis at 7, 44; Dn. truncata at 53, 54; E. kanawhaensis at 44; 

 and P. phyma at 3, 5, 7, 24, 44, and 64. 



