288 MR. J. W. KIRKBY ON SOME 



Possneck appears to consist of four bocly-rings and the two pos- 

 terior segments.* I have been fortunate, however, in procuring 

 one specimen showing the cephalic segment or carapace, with 

 two body- segments attached. (PI. XII. figs. 1, 2, 3.) 



The carapace is about as long as four of the succeeding body- 

 rings, somewhat less in depth, and slightly compressed laterally ; 

 it is carinated along the back, and wedge-shaped in front; the 

 eyes are large, round, and prominent, and are placed far for- 

 ward ; from the lower part of each eye runs an indented line, at 

 a short distance from the margin, up to the dorsal region, where 

 it curves forward. 



The other five specimens consist of bod^^-rings (2 to G in num- 

 ber) and the two great posterior or caudal segments ; "f and are 

 very similar to the figures given by Schauroth. In one of the 

 Durham specimens (fig. 7) there are six body-rings, and two 

 posterior segments ; the others (figs. 4, 5, 6) have likewise the 

 two latter segments, but not so many of the former. The body- 

 segments are narrow, almost uniform in size, but varying a little 

 in depth, the central ones appearing to be the most produced ; 

 they overlap each other and the penultimate segment posteriorly ; 

 they are slightly compressed, and have traces of a median dorsal 

 ridge ; those in front have their extremities turned a little for- 

 ward, while the posterior ones are bent in the contrary direction. 

 The large penultimate segment is greatly developed laterally ; it 

 is strongly carinated dorsally ; its ventral margins are slightly 

 convex, as is also the posterior border, which has a deep notch 

 not far from the dorsal ridge ; the ridge or keel of this segment is 

 very prominent except anteriorly, where at each side of the dor- 

 sal line is a transverse swelling ; it is compressed also posteriorly. 

 The next segment, which is the hindermost known, is more com- 

 pressed than the preceding one, and considerably smaller. 



None of the English specimens show the true external surface, 

 nor have any traces of feet or of antennae been found. 



The specimen with the carapace (figs. 1-3) is one-eighth of an 



* The latter are rcffarded as the cephalic and thoracic segments l)j- this author, 

 t It is probable that we have all the hintler segments in these specimens; but there may 

 possibly be a small terminal one besides. 



