242 MECZNIKOW, ON ICHTHYDIUM, ETC. 
From the foregoing it will be seen that the Ichthydina 
form an interesting, but, as yet, little known group of animals. 
Ehrenberg has described three species belonging to the 
genus Chetonotus, to which Dujardin adds a fourth, Cheto- 
notus tesselatus. The diagnoses and descriptions of these 
naturalists are too incomplete to determine certainly the 
differences of species; hence later naturalists, as Perty and 
Schultze, have merely guessed the identity of the above- 
mentioned species. As for the forms described by Ehren- 
berg, I think I am right in uniting them in a single 
species under the name of Chetonotus larus, whose chief 
character consists in the form of the dorsal bristles, which 
are not, as those described by Schultze, formed of two diffe- 
rent parts, but consist of one single, simple, crooked bristle. 
That form which is described by M. Schultze, and most 
likely also by Perty, as Chetonotus maximus, must be con- 
sidered as a new kind, and therefore may well be named 
Chetonotus Schultz. If now it is considered that the dorsal 
bristles are the criterion of species among the forms belong- 
ing to the genus Chetonotus, one must consider that de- 
scribed by Dujardin as Chetonotus tesselatus, as a distinct 
species; and, in fact, this kind (of which I have found not a 
few in Charkow and in Giessen) differs remarkably from all 
others, in the peculiarly scaly form of its dorsal bristles. 
Besides these, I know another form of Chetonofus which I 
consider new, because of the peculiar form of the back 
bristles, one of which I have figured in fig. 6a. This form, 
which was found in the marshes of Giessen, I name 
Chetonotus hystrix ; it is 0°12 mm. long. 
Of the genus Ichthydium I know a new one which was ex- 
amined by me in the province of Charkow, and which from 
the peculiarities it presented I name Ichthydium ocellatum. 
This bottle-formed species as represented in fig. 4 is pro- 
vided on the forepart with some pretty long hairs, and, besides 
this, with a ciliated covering on the ventral surface. 
Besides the two forms just mentioned, I have noticed two 
which I consider to be representatives of two peculiar genera. 
One of these is stretched longitudinally, and not bottle- 
shaped, as Chetonotus, Ichthydium, and my other new genera ; 
the head is in fact somewhat broader than the rest of the 
body ; the back is provided with elevations which are placed 
one after the other. The ventral surface is covered with a 
tunic of cilia; on the back of the tail-end there is a row of 
strongly bent bristles. On the hind part of the body there 
are two dichotomous furcal appendages which are very cha- 
racteristic of the animal. 
