450 Illinois State Laboratory of Natural History. 



The nephridia closely invest the ventral vessel, and, so far 

 as observed, but one nephridium is contained in a somite. 



The sperm-ducts have no prostate gland, atrium, or penis, 

 and open into a median spermiducal chamber on the ventral 

 side of XI. 



A pair of sperniathecre is present in the anterior part of X, 

 and the spermathecal pores are a considerable distance from 

 each other. 



A pair of elongated tubular glands is present in IX, opening 

 in close relation with the genital setae of that somite. 



No attempt has been made to distinguish between generic 

 and specific characters, since only one species of the genus 

 is known. From the foregoing it is apparent that Rhizodrilus 

 lactejis is somewhat closely related to Lumbriculus spiralis of 

 Leidy ('52a, p. 285) in respect to length, number of somites, 

 form and character of seta?, color, and habits ; but as Leidy's 

 description is entirely inadequate for the purpose of identifi- 

 cation, and as he left no type specimens of his species, the 

 relationship between the two forms cannot be determined. It 

 is unfortunate that the description of a new species of Tubi- 

 ticidic so frequently involves the description of a new genus, but 

 according to present ideas of the classification of this family 

 the character of the species under discussion will not permit 

 its inclusion in any existing genus. The presence of two 

 distinct kinds of highly modified genital seta? and the pres- 

 ence of such seta? in the ninth somite distinguish this worm 

 from all other described forms of Tubificida. In the absence 

 of distinct prostate glands and in the presence of a common 

 spermiducal chamber it differs from most Tubificidee but 

 resembles Vermiculus. There is a farther resemblance to the 

 latter genus in the simplicity of the longitudinal blood-vessels 

 and in the absence of both supra- and sub-intestinal vessels, 

 but the relation of the lateral vessels of the anterior somites 

 to other parts is very different in the two genera. In Vermic- 

 ulus pilosus, in II-X there is no direct communication 

 between the dorsal and ventral vessels, the single pair of 

 branches of the dorsal vessel in each of those somites break- 

 ing up into a capillary network in the body wall, from which 



