MECZNIKOW, ON ICHTHYDIUM, ETC. 249 
give any conclusive result as to the nature of these remark- 
able animals ; therefore my wish is only to amplify or correct 
some conclusions of Claperéde, which merely touch upon the 
outside skeleton. 
The body of our animal (Hchinod. Duj.) is convex on 
the back, and, on the contrary, concave on the belly, so that 
the diameter shows a kidney-like form. The three foremost 
segments differ in that they seem to be convex on the ventral 
surface. The first body-segment consists of a thin lamella, 
which is provided with perpendicular thickenings of the 
cuticula, with a bending character, and which therefore 
differs from all the other rings. It is a formation which is 
obviously necessary for the pushing in and out of the snout- 
like head. The following segment possesses a strong cuticula, 
which is simply thickened on the upper edge, and which 
shows on the lower edge a fine marking. The markings 
resemble thickened stripes on the edge of the cuticula, 
and form in no way, as Claperéde represents, “a girdle of 
stiff bristles, which arise from different pieces of chitin.’ 
The third, which is also biconvex, differs from the others 
principally because on its thickened ring begins a division 
into sections. ‘Two tergal pieces are formed by a looping on 
the middle line in the back, which pass to the side parts of 
the body, and stop again at two symmetrical loops of the 
unequal sternal portion. On the back surface of the third 
segment is a middle unpaired tuft of bristles. 
The skeleton commences only in the fourth segment, and 
does not occur, as Claperéde states, in every segment but the 
first. Here the sternal plate splits itself into two separate 
pieces by a deep crack which lies in the middle of the 
body, formed by bending in the concavity of the ventral sur- 
face. In this segment, as well as in all following, the above- 
mentioned indentation, which divides both the tergal portions, 
can be plainly seen—a fact which Claperéde has quite over- 
looked, as he described the whole skeleton as consisting of 
only one tergal and two sternal parts. 
The formation of the skeleton as described by me in the 
fourth is true for all the following, and for the last or furcal 
segment which is formed by two plates. The strong ventral 
and more weakly marked dorsal indentations both continue 
to the end of the body. The furcal parts carry on both 
sides a long and a shorter tuft of bristles, which, like the 
bristles on the penultimate segment, arise from the ridge of 
the skeleton. But the other bristles are placed very diffe- 
rently. In the middle of the back, in the neighbourhood of 
the dorsal indentation, there is a bristle from the third to the 
VOL. VII.—NEW SER. s 
