1905.] NATURAL SCIENCES OF PHILADELPHIA. 375 



those described recently by other authors, tend to traverse some of the 

 generic boundaries visually set up and to obscure their limits, Tuhifex 

 is here employed in a broad sense, and it will be noticed that T. irro- 

 ratus approaches Monopylephorus in many respects and removes that 

 genus from the isolated position that it has been considered to occupy. 

 This species resembles Monopylephorus in its valvular and moniliform 

 blood-vessels, the form of its nephridia and the short sperm ducts 

 with diffuse prostate glands. On the other hand, the paired genital 

 orifices, the well-developed penes and the capillary setae in the dorsal 

 bundles are characters of Tuhifex. Ditlevsen has referred to Monopy- 

 lephorus a species (M. trichochcetus) having all of these characters 

 except the penes. The supposed great gap between these genera is 

 thus bridged by two species. On the other hand, Tuhifex hamatus, 

 which is in most respects a typical Tuhifex of the Psanimoryctes group, 

 appears to lack capillary setae altogether. Some of our forms here re- 

 ferred to European species exhibit slight departures from the published 

 descriptions, and it is possible may prove to be distinct when actual 

 comparison of specimens from both places comes to be made. Besides 

 the species described in this paper my collections include several others 

 represented only by immature specimens, from which the characters of 

 the reproductive organs cannot be ascertained. 



The following key will facilitate the determination of species noticed 

 in this paper: 



A. — Asexual reproduction by serial budding and fission. 



B. — Spermathecae in V; setae all hooked and bifid, the dorsal 

 bundles beginning on V; size very small, 



Paranais littoralis. 

 AA. — Reproduction normally by the sexual method only. 



BB. — Spermathecae in V; setae all with simple (not bifid) tips and 

 dorsal bundles beginning with the ventral on II; male 

 pores on XII. 

 C. — Setae /-shaped ; blood yellowish; testes deeply lobulated, 



Lumhricillus agilis. 

 CC. — Setffi straight, with hooked internal ends; blood color- 

 less; testes not subdivided, . Enchytroeus alhidus. 

 BBB. — Spermathecae in X; setae more or less distinctly bifid at the 

 tips and of various forms, often associated in the dorsal 

 bundles with capillary setae; male genital pores on XI. 

 D. — Male genital pores and spermathecal pores paired ; 

 penes present. 

 E. — Atrium simple; no special prostate gland; 

 spermathecae reaching into XI when fully 

 developed, Clitellio arenarius. 



