1892.] AQUATIC OLIGOCH^TOUS WORMS. 355 



contractile. This species is, of course, freshwater in habitat. It 

 was found in a forest-pool along with Phreoryctes smithii. 



None of the specimens were mature, so I am unable to say how 

 far they may agree with Clitellio in other particulars ; but, in any 

 case, they have the two pairs of dilated vessels in viii. and ix. that 

 have hitherto served to distinguish Clitellio from Limnodrilus. 



V. On a new Genus (Kerria) intermediate between Acanthodrilus 

 and Ocnerodrilus. 



Mr. J. Graham Kerr, who accompanied the " Pilcomayo Expe- 

 dition "in 1890, has kindly given me a number of small Oligochaeta 

 which he collected in the upper reaches of that river. They were 

 preserved with corrosive sublimate, and are in consequence in an 

 excellent condition for microscopical examination. There are alto- 

 gether about a dozen specimens, some fortunately being sexually 

 mature. The water where they were met with was exceedingly salt 

 and bitter, but contained a number of other animals, notably a few 

 decapod Crustaceans. But animal life was not, Mr. Kerr informs 

 me, very abundant in the stream. So far as I am aware, no Oligo- 

 chaete of any kind has ever been described from a locality like the 

 present, except a species of Pachydrilus referred to by Semper as 

 occurring in the brine-springs of Kissingen in Germany, Salt water 

 is not, however, entirely inimical to the existence of Oligochaeta, 

 for there are a few species known from the sea-shore ; for example, 

 Clitellio, referred to in the present paper, Pontoscolex, Pontodrilus, 

 &c. I expected, therefore, that these worms would prove to be 

 interesting, and my expectations were realized. 



The worms are all very small, an inch to an inch and a half in 

 length by I mm. in diameter. They are about the size of, and re- 

 semble in general appearance, Ocnerodrilus eiseni, and I at first was 

 disposed to refer them to the same genus at least. Although a 

 more careful examination of the worms showed that they could not 

 be referred to the genus Ocnerodrilus, it became very soon evident 

 that they were nearly related to that genus ; they serve, in fact, to 

 indicate the probable relations of Ocnerodrilus, concerning which I 

 was formerly in doubt '. Eisen, the original describer ^ of the genus 

 Ocnerodrilus, placed it in the family Lumbriculidae. This conclusion 

 was subsequently abandoned by Eisen himself ^ and I have myself^ 

 endeavoured to combat it ; the genus is clearly to be referred to that 

 very large and imperfectly known group of worms which I have 

 called Cryptodrilidse. I do not propose to give a detailed systematic 

 account of the anatomy of this new worm, but merely to dwell 



* "On the Anatomy of Ocnerodrilies (Eisen)," Tr. Roy. Soc. Edin. vol. xxxvi. 

 No. 21. 



^ "On the Anatomy of Ocnerodrilus" Nov. Act. Reg. Soc. Upsal. ser. 3, 

 vol. X. 



^ " On the Anatomy of Sutroa rostrata, &o.," Mem, Calif. Ac. Sci. vol, ii, 

 no. 1. 



* Loc. cit. p. 580. 



