306 OLIGOCHAETA 



As to the species of the genus, VAILLANT allows seven ; but two of these are, 

 as he himself admits, doubtful ; the two doubtful species are Ch. JUiformis of SCHMAKDA 

 and the Derostoma laticeps of DUG is. With regard to the former, which is figured, 

 though very insufficiently, it is certainly a member of the genus. SCHMABDA figures 

 setae upon evei-y segment of the body. It comes from Curaca, in South America ; 

 I have examined a specimen from Valdivia. Derostoma laticeps, at first referred by 

 DUGES to the Planarians, was afterwards (3, p. 30) placed in the genus Nais ; but no 

 particulars are given save that there is only a single set of setae on each side of the 

 body, and that the 'lip' is large (suggestive, as VAILLANT has pointed out, of an 

 Aeolosoma). Whether Ch. gulosus of LEIDY (3, p. 124) is a 'good' species or not 

 seems doubtful. There is really nothing in the description which is at all decisive 

 in the matter. Its length is one line, and there are five or six setae in each bundle. 

 The oesophagus is said to be short. 



I allow the five following species, and I use VEJDOVSKY'S names. This because 

 it does not seem to me to be possible to identify the Nais vermicular is of MCLLEB. 

 The only distinguishing feature of it is its length (2 lines). That possibly brings it 

 nearer to Ch. diastrophus, but the identification does not appear to me to be certain. 



(i) Chaetogaster limnaei, v. BAEB. 



Ch. limnaei, v. BAEB, Nov. Act. Nat. Curios., 1827, p. 61 1. 



Ch. furcatus, EHBENBERG, Symb. Phys., 1828. 



Ch. diaphanus, OEBSTED, Nat. Tidsskr., 1842, p. 138 (in part.). 



Ch. vermicularis, GBUBE, Arch. f. Nat, 1851, p. 353 (in part.). 



Mutzia heterodactyla, VOGT, Arch. f. Anat. Phys., 1841, p. 36. 

 Definition. Length, 2 mm. ; oesophagus much reduced. Hob, Europe. 



This species lives parasitically upon fresh-water Mollusca and sometimes within 

 their bodies. It is the smallest species of the genus. The anterior pair of setae 

 are commonly somewhat stronger than the rest. The first pair of nephridia open 

 in front of the second setae bundles. 



(2) Chaetogaster diaphanus, GEUITHUISEN. 

 Ch. niveus, EHRENBEEG, Symb. Phys., 1828. 

 Ch. diaphanus, OEBSTED, Nat. Tidsskr., 1842, p. 138 (in part.). 

 Ch. vermicularis, GKUBE, Arch. f. Nat., 1851, p. 353 (in part.). 

 Nais diaphana, GRUITHUISEN, Nov. Act. Nat. Curios., 1828, p. 409. 

 Nais lacustris, DALYELL, Powers of Creator, vol. ii, 1853, p. 130. 

 Nais scotica, JOHNSTON, Cat. Worms B. M., 1865, pp. 71 and 336. 



