1888.] STRUCTURE OF CLITELLIO. 487 



the principal one which differentiates the genus from Tubifex, and is 

 recapitulated by Vejdovsky in the systematic part of his great work 

 upon the Oligochseta^ I find that in Clitellio ater the setse of 

 the dorsal pair are sometimes of two kinds — (1) bifid setae, (2) long 

 slender setee (Haarborsten). On the other hand, the ventral setse 

 belong only to the bifid form. This, however, is not always the 

 case ; individuals of C. ater are frequently met with which possess 

 only the bifid setse ; these individuals were indistinguishable in any 

 other character from those in which hair-setse were also present. 

 The character of the setse must therefore be regarded as variable. 

 As to the number of setse per bundle, I find that there are usually 

 two, though sometimes more. 



§ 1. Remarks on some other Marine Species of Tubijicidce. 



Besides these two species, a considerable number of marine 

 Tubificidse have been described from the Western European coasts. 

 These are : — 



Tubifex benedii, d'Udekem, " Nouv. Class. Annelides Setigeres 

 Abranches," Bull. Ac. Roy. Belg. t. xxii. (1855), p. 544. 



T. hyalinus, id. ibid. 



T.papillosiis, Claparede, Beobachtungeniiber Anat. und Entwick. 

 wirbellos. Thiere an der Kiiste von Normandie angestellt. 

 Leipsic, 1863. 



T. lineatus, Miiller, Zoologia Danica. 



T. bilineata, Montagu, MS. ; Parfitt, " Catalogue of AnneHds 

 of Devon," Trans. Devon. Assoc. 1867, ii. 



T. pellucidus, Montagu, MS.; id. ibid. 



Peloryctes inquilina, Zenger, Bull. Soc. Imp. Nat. Moscou, xliii. 

 pt. 1 (1870), p. 221. 



The first two species are considered by Tauber " to belong to the 

 genus Limnodrilus, for the reason that they only possess bifid setse, 

 a fact noted by d'Udekem in his brief description of the species. I 

 believe him to be wrong in this identification ; there is nothing in 

 d'TJdekem's description to prevent both these species from being 

 included in the genus Clitellio, which, and I can confirm Claparede, 

 is also characterized by the absence of hair-setae. Furthermore 

 Clitellio and Limnodrilus also agree in the possession of two pairs 

 of "hearts," situated in segments 7 and 8 respectively. Claparede only 

 observed one pair in C. arenarius, whose position he was unable to fix 

 with accuracy. I have, however, seen two in living specimens, where 

 they are very distinct. The presence of two pairs of specially dilated 

 vascular arches has been described in the European species of Limno- 

 drilus, and I have had the opportunity of verifying this character of the 

 genus in a New-Zealand species, which may or may not be identical 

 with one or other of the European species. The two genera can only 



^ System u. Moi-phologie der Oligocbaeteu, p. 45. 

 ^ ' Annulata Danica,' p. 71. 



