316 PROCEEDINGS OF THE NATIONAL MUSEUM vol. lu 



it bifurcates into the large deferent lobes which then proceed ventro- 

 mesad into the deferent ducts. Prostate gland similar in length, 

 diameter, and external appearance to the spermiducal gland, and 

 likewise is directed entally first dorsad and then ventrad, crossing 

 over the flexed part of the spermiducal gland in changing its direction ; 

 extending ventrad to level of the posterior deferent lobe. 



Spermatlieca is composed of three distinct sections: The basal or 

 ectal half is an elongate, sinuous, muscular duct merging into a some- 

 what enlarged, subgiobose, clear-waUed ental bulb, this in tm-n gives 

 origin to a smaller, tubular, and strongly glandular ental process, 

 terminating in a rounded, somewhat swollen tip. 



Variation. — This species is known only from a single collection of 

 about a dozen worms, these vaiy among themselves only in size and 

 proportions. In smaller worms, the dental formula is more consist- 

 ently 5-4, the outermost lateral cusps of the dorsal jaw tending to be 

 worn away in old specimens. 



Affinities. — Among known species of the genus, this one is ob- 

 viously closest to O. macrocejihala, and the differences between the 

 two are largel}^ set forth in the diagnoses and in the key. The 

 presence of distinct tentacles will easily preclude confusion of holti 

 with mesochorea, the only other eastern member of the section of 

 comparable size and with very large, undifferentiated prostate gland. 



Distribution. — Known only from the type locality, "a medium 

 large mountain stream" on the southern outskirts of Somerset, 

 Kentucky. Perhaps it thus partakes of the characters of a more 

 mountainous habitat than might be expected in south central Ken- 

 tucky. It is unusual that numerous other collections made in the 

 same general region on the same day did not yield specimens of this 

 form. That it is endemic to a single stream seems unlikely, and the 

 resolution of its distribution and ecology stands as a challenge to some 

 future student of the genus. 



Remarks. — C. holti was taken in association with species in the 

 genera Pterodrilus and Xironodrihis . The iypa specimen and some 

 of the para types are rather heavil}'' infested with stalked colonial 

 peritrich protozoans, much more than any other specimens examined 

 during this study. 



BRANCHIOPHILA GROUP 



This group embraces two species of somewhat dissimilar worms, 

 and may liave to be abandoned when the genus becomes better known. 

 Both of the species are small and although generally similar in structure 

 may not share a common origin. 



In this group the spermiducal gland is of normal relative size and 

 proportions, and produced into a large terminal or lateral posterior 



