34 Proceedings of the Biological Society of Washington. 



follows: Lumbricus lacustris Verrill, sp. nov. About 1.5 inches 

 long, 0.04 in diameter. Body round, distinctly annulated. 

 Head short, conical, obtusely pointed. Setae spine-like, 

 strongly curved, acute, arranged two by two, those of each 

 pair close together. Color reddish brown. 



Of these characters some apply equally well to both species. 

 "Body round, distinctly annulated"; " setae * * * ar- 

 ranged two by two, those of each pair close together"; are of 

 this class. The applicability of statements concerning the length 

 and color can not be judged, because of the poor state of preser- 

 vation of the material. The diameter (0.04 inch) is correct 

 for the specimens of Mesoporodrilus, but that dimension in 

 the Lumbriculus specimens is scarcely three-fourths as great. 

 The description of the setae (spine-like, strongly curved, acute), 

 is more nearly correct for the Mesoporodrilus specimens, since 

 the setae of the others are cleft at the outer extremity. The 

 description of the prostomium probably more accurately fits 

 the specimens of Lumbriculus, although applicable to the 

 others in their poorly preserved condition. 



It seems reasonable to assume that the description really 

 combines characters of the two species, but it more nearly fits 

 the specimens of Mesoporodrilus. Lumbriculus inconstans 

 has had frequent mention in literature for something over 

 twenty years. Under the circumstances the writer prefers to 

 associate Verrill's species name with the specimens of the other 

 genus which will accordingly be described as Mesoporodrilus 

 lacustris (Verrill) F. Smith. 



This paper is No. 128 of the series of contributions from the 

 Zoological Laboratory of the University of Illinois. 



Mesoporodrilus F. Smith. 



Setae closely paired; simple. Clitellum on 10-12 and part or all of 9 

 and 13; complete ventrad. Spermiducal pore on 10; median. Oviducal 

 pores paired; in 11/12; in line of ventral setae. Spermathecal pores median; 

 anterior to spermiducal pore. Spermaries and spermiducal funnels paired; 

 in 10, or in 9 and 10. Atrium elongated; differentiated into a muscular 

 sperm reservoir and relatively small penial organ, connected by a con- 

 torted duct. Ovaries and oviducal funnels paired in 11. Spermathecae, 

 one or two; asymmetrical in position; opening on 9 or on 8 and 9. 



Type species, Mesoporodrilus asymmetricus F. Smith. 



