298 OLIGOCHAETA 



four: viz. D. latissima, D. perrieri, D. mutteri, and D. acuta, are described for the 

 first time by himself and not noticed by VAILLANT. The remaining three are D. 

 obtusa, D. limosa ( = D. philippinensis), D. furcata (=D. palpigera, and D. rodriguezii) ; 

 D. digitata (Nais digitata, O. F. MULLER) is mentioned as ' doubtful.' 



The species iiot referred to by BOUSFIELD, but included in this genus by VAILLANT 

 are Pristina flagellum of LEIDY, Aulopltorus oxycephala of SCHMABDA, Xantho decapoda 

 of DUTEOCHET ; D. palpigera and D. pJdlippinensis are considered to be distinct species. 

 P. flagellum does not seem like to be referable to the present genus by reason of 

 the fact that the dorsal setae commence from the very first that there is no 

 cephalization like that of Dero. It is just possible that P. flagellum belongs to my 

 genus Branchiura, D. decapoda is too imperfectly known to permit of its being regarded 

 as a distinct species. It is said to have ten appendages from the branchial area. 



D. palpigera is so imperfectly described by GREBNITZKY that I have no wish to 

 criticize the view advanced by SEMPER that it is the same as his D. rodriguezii, 

 and by BOUSFIELD that both are identical with D. furcata. 



It is very difficult to identify Xantho hexapoda of DUTROCHET, Nais auricularis 

 of Bosc, which BOUSFIELD regards, and with great probability as a Dero, and Aulo- 

 phorus discocephalus of SCHMARDA. No doubt BOUSFIELD is also right in stating that 

 it is impossible to identify D. digitata of MULLER. I do not admit for the present 

 D. stuhlmanni of STIEREN. The only distinctive character appears to be its very 

 small size (2 mm.), though size is sometimes, I believe, a reason for specific distinction. 



D. intermedia of CRAGIN is doubtful. Nais caudata of SCHMARDA, with lengthened 

 posterior segment, may also be a Dero. 



(i) Dero mtilleri, BOUSFIELD. 



D. mulleri, BOUSFIELD, J Linn. Soc. 1886, p. 104. 



Definition. Length, i^mm.; number of segment* 95. Branchial processes, oblong, quadrangular, 

 loicer longest. Hearts usually seven pairs. Hob. Great Britain. 



This species is easily to be distinguished on account of the peculiar form of the 

 branchial processes. 



(2) Dero limosa, LEIDY. 



D. limosa, LEIDY, Am. Nat. 1880, p. 421. 



D. philippinensis, SEMPER, Arb. Zool. Zoot Wurzb. 1877/78, p. toy. 

 D. acuta, BOUSFIELD, Kep. Brit. Ass., 1885, p. 1098. 

 Definition. Length, 6 mm.; number of segments 60. Branchial area with, dorsal lip which 



