292 MU. J. W. KIRKBY ON SOME 



Notes added since the preceding Paper ivas coimmmicated to the 

 Geological Society. 



1. Prosoponiscus Problematicus, Schloth. 



Since the preceding remarks were written I have found an- 

 other specimen of this interesting species. Like the others, it is 

 fragmentary ; but as it is the anterior portion of an individual , 

 and possesses the carapace, with four of the body-rings attached, 

 it is not without importance. It is, allowing for two additional 

 segments, about twice the size of the anterior portion figured. 

 The size of the carapace, compared with that of the body-rings, 

 scarcely appears to be so large in this example as in the former. 

 This in some measure seems to be due to the extension of the 

 segments, the individual having been incurved, consequently the 

 body -rings are drawn out, and their length seems to be greater, 

 in proportion to their depth, than those of figs. 1 and 2, which 

 represent these segments as overlapping. But allowing for a 

 greater exposure of the body-rings in the larger specimen, the 

 carapace is still, in a relative sense, of smaller dimensions than 

 the other ; in other respects the specimen agrees with the former. 

 The carapace is of similar form, and is marked with the same 

 marginal indentation. The eyes are as far forward, and just as 

 prominent; and both the carapace and the body-rings are cha- 

 racterised by a dorsal ridge. 



It is to be hoped that a perfect example of this rare species 

 will shortly be discovered, or at least a specimen or specimens 

 more perfect than those hitherto found, so that we may know 

 the true relation which the large penultimate segment bears to 

 the body -rings, and the number of these which intervene be- 

 tween it and the carapace. Such a specimen would also set at 

 rest all doubts as to the specific identity of the two series of 

 fragments — the anterior portions, and those I have termed pos- 

 terior. However, as yet, it seems safer to refer both to one 

 species than to consider them distinct, for though they may 

 possibly belong to different species, yet when we consider that 

 the posterior segments of the one are in all respects identical 

 with the anterior of the other, it seems more likely that we have 



