Species of North American OUgocIujeta. 287 



of the D. riparia from Havaua shows clearly that they 

 belong to distinct species; but it is necessary to revise* 

 somewhat the list of differences as given on p. 148 of 

 my earlier paper (12). 



The two species agree in the presence of a pa-.r of very 

 small nephridia opening upon II, and also in the posi- 

 tion of the first dorsal pore, which is in the anterior 

 part of XI. 



The principal characters which distinguish the species 

 are as follows: (1) The spermathecal pores are pos- 

 terior to the set£B in D. eiseni, while they are anterior 

 to the setae in D. riparia; (2) the ventral setae of VIII 

 and IX in D. eisini are modified and accompanied by 

 glandular sti-uctures, while in D. i^iparia. they are not; 

 (8) the ventral sette of XIX are one or both present 

 on each side of the somite in D. eiseni, but both are 

 lacking in D. riparia; (4) the quadrangular glandular 

 area upon the ventral part of XVIII — XX described by 

 Michaelsen in D. eiseni is quite conspicuous in that 

 species, but is not noticeable in J), riparia; and (5) 

 the two species are very different as regards size. On 

 this latter point I may say that the specimens of D. 

 ■eiseni received by me were quite uniform in size, and 

 that none of them had a length of more than 150 mm. 

 when alive and full}' extended, the diameter of the an- 

 terior part being only 2 mm. and that of the other 

 regions still smaller. Michaelsen, on the other hand, 

 gives 160 mm. as the length of one of his specimens 

 and 3-3.5 mm. as the diameter, but this seems to have 

 been exceptional, since he states that "andere Stiicke 

 eind betrachtlich kleiner." Ordinary specimens of D. 

 riparia are 220-250 mm. in length when fully extended, 

 and 3 mm. in diameter. By comparing average speci- 

 mens of each species I find the ratio between the weights 

 of individuals of D. riparia and of those o\ D. eiseni to 

 be more than 5:1. 



