360 PROCEEDINGS OF THE NATIONAL MUSEUM vol. ii4 



Description. — ^A small worm reaching a maximmn length of^about 

 2.0 mm. in preserved specimens. Body form slender, the diameter 

 increasing gradually to segment vi which is subequal in bulk to seg- 

 ments VII and VIII ; caudal sucker somewhat larger than preceding 

 segment and about as broad as the peristomium. Prosomites up to 

 three times as long as the metasomites, but not of greater diameter. 



Head about as long as the first three body segments combined, and 

 equal in diameter to segment iii, the peristomimn set off by a very 

 strong basal constriction and distinctly flared, its margin entire, 

 without any trace of division into dorsal and ventral halves or into 

 smaller lobes. Head otherwise not visibly segmented externally. 



Jaws similar, dental formula 3-3 with the median tooth long and 

 acute, the general appearance very similar to the jaws of C. fallax 

 but the formula perhaps more often 3-3 than in that species. 



Male reproductive system basically simiiar to that of other species 

 of the Philadelphica group. Bm^sa rather long, equaling the length 

 of the spermiducal gland, the two subequal in diameter. Ejaculatory 

 duct modest in size, its length less than the diameter of the spermiducal 

 gland. Latter of normal proportions, without evident lobation at 

 entry of deferent ducts. Prostate long, slender, about half the 

 diameter of spermiducal gland, which it joms slightly entally of the 

 entry of the ejaculatory duct. 



Spermatheca slender and elongate, curving laterad and dorsad 

 around the gut, and becoming slightly wider but maintaining about 

 the same diameter almost to its end at a pomt near the middorsal 

 area of the segment, a distinct ental bulb not bemg well-developed. 



Variation. — In the small amount of material examined from three 

 localities, some of it not well-preserved, there appeared to be little or 

 no variation in the diagnostic characters of the species. 



Affinities. — The relationships of this form with C. fallax and 

 C. philadelphica, with both of which it is sympatric, are unquestion- 

 able. It differs from both, however, in characters of the peristomium 

 and spermatheca. Closer relationship with fallax is postulated on the 

 basis of jaw form, here considered to be a more fundamental character 

 than peristomial lobation. 



Distribution. — ^Aside from the type locality, this species is known 

 from two collections from western Virgiuia, in the James and upper 

 Potomac River dramages. 



Virginia: craig county: 1.5 miles south of Paint Bank on Va. Hy. 311, June 24, 

 1948, Horton H. Hobbs (PCH 97). rockingham county: Swift Run, 3 miles 

 east of Elkton on U.S. Hy. 33, December 12, 1946, Holt (PCH 14). 



Remarks. — Fm^ther knowledge of the distribution of this localized 

 form may be of interest in providmg an insight into the factors influenc- 

 ing its speciation. 



