DESCRIPTIONS OF GENERA AND SPECIES 265 



phores are to be found i. Vaillant eliminates /. coccineus from the genus Ilyodrilus, 

 restricting the genus to the three American species, remarking (6, p. 349) that the 

 former is, according to Vejdovsky, merely a variety of T. rivulorum; this was 

 certainly Vejdovsky's original opinion when writing his great monograph ; but in a 

 footnote to a later page (p. 156) of that monograph, he distinctly refers to I. coccineus; 

 by this time, no doubt, Stolc had completed his researches on the worm, proving 

 its distinctness from Tubifex; hence the footnote, probably added as the work was 

 passing through the press. Eestricting the genus, as I propose to do here, it will 

 contain only one species — /. coccineus. 



Eisen's genus Ilyodrilus will not, I think, stand ; the three species of which it is 

 composed are not, in my opinion, referable to the same genus so long as we allow 

 the numerous genera adopted in the present work; the differential characters of the 

 genus, as given in Eisen's work upon the Tubificidae, by no means apply to all the 

 species; the only character that does so apply, and is of real importance, is the 

 absence of spermatophores ; I should venture, however, to doubt the real absence of 

 the spermatophores, since the three species all of them possess prostates; in all 

 Tubificidae, with the exception of Teliniatodrilus^ which have prostates, there are 

 spermatophores formed. Another character used by Eisen in the generic description 

 is the absence of glands at the base of the spermathecae ; there are, however, such 

 in 'Ilyodrilus' sodalis; can this species be put anywhere than in one of the genera 

 Tubifex or Hemitubifex ? The glands at the base of the spermathecae ally it to the 

 latter, from which the absence of a vesicula seminalis distinguishes it. In this it 

 agrees with Tubifex, and in having a soft penis without chitinous sheath. As in 

 both genera there are no pectinate setae; in the species under discussion the two 

 prongs of the uncinate setae have fine denticulations along the inner margin, but 

 these setae are hardly comparable to the pectinate setae of other genera. I am 

 disposed to refer this species to the genus Tubifex, in spite of the presence of 

 glandular appendages to the spermathecae. ' Ilyodrilus ' perrleri, unlike the last 

 species, and unlike Tubifex, has a chitinous sheath to the penis ; there is a very 

 faintly developed pectination of the uncinate setae ; this species seems to come 

 nearest to Hemitubifex. '■Ilyodrilus' fragilis is the only remaining species of 

 Eisen's genus ; it must go, I think, with the last into the genus Hemitubifex (as 

 Vaillant has suggested). These three species seem to unite the genera Tubifex and 

 Hemitubifex. Apart from these species the two genera in question are separated by 

 very slender characters. In Tubifex the penis is soft, and there is no vesicula 



' Vejdovsky (24, Taf. iv. fig. 13) has figured the spermatophore of I', cocdnms, but it is to fee presumed that 

 this is an error. 



M m 



