XortJi Aino'icaii Liimhriciil'dw. 475 



oviducal pores in the anterior part of XII. These dilt'erences 

 seem siifiicient to warrant the recognition of the species as 

 generically distinct from the other two. 



M. asymmctricus and P. pahistris are more closely related 

 to each other than is either of them to E. frigidiis. They, 

 alike, have (l)a prostomium, (2) but one pair of nephridia 

 anterior 'to the reproductive organs, (3) unpaired nephridia 

 posterior to XII, (4) one pair of testes, (5) two pairs of 

 lateral vessels in each of the somites posterior to X, and (6) 

 no perigastrics ending blindly in the crelom. They differ 

 from each other in several important respects, as follows : 

 (1) in the position of the anterior nephridia, (2) in the 

 position of all the reproductive organs, (3) in the number of 

 sperm-ducts and spermiducal funnels, (4) in that the pros- 

 tate and atrium of M, (ist/)nnu'triciis seem to be replaced in 

 P. j^altistris by a greatly developed penial apparatus, (5) in 

 the position of the spermiducal pores, (6) in the symmetry 

 or asymmetry of the sperm-sacs, (7) in the structure and 

 proportions of the spermathecte, (8) in the position of the 

 spermathecal pores, and (9), in a marked manner, in the 

 relations of the lateral vessels. As already intimated, only 

 future collections and study can make it possible to determine 

 whether these differences ought to be regarded as generic or 

 as merely specific ; but, all things considered, it seems .the 

 wiser plan at present to regard the two species as generically 

 distinct. 



The writer takes this opportunity to acknowledge his obli- 

 gations to Mr. Hempel for his kindness in obtaining the 

 specimens of the new species described ; to Dr. Gustav Eisen 

 for several specimens of Eclipidriliis; and to Prof. S. A.Forbes 

 for the opportunity to study a species of Si(tro<( collected l)y 

 him in Yellowstone Park. The drawings for the figures were 

 made by Miss Lydia M. Hart, Artist of the Illinois State 

 Laboratory of Natural History. 



University of Illinois, May 19, 1900. 



