158 Dr. W. T. Caiman — Pleurocaris, a new Crustacean 



The abdomen, excluding the telson, is longer than the seven thoracic 

 •somites together. The six somites increase in length from before 

 backwards, and the pleural plates, horizontal and square-cut like the 

 posterior thoracic pleura on the first somite, become bent downwards 

 and acutely pointed backwards on the posterior somites. The abdomen 

 thus appears narrowed posteriorly, but the actual width of the somites 

 is apparently not very different from that of the thorax (1-4 mm.) 

 if the pleural plates be excluded. The dorsal surface is ridged or 

 annulated like that of the thorax, the ridges increasing in number 

 from about three on the first somite to about five on the fifth. The 

 exact number of ridges, however, is difficult to make out, owing to 

 crushing and to the obscure delimitation of the somites. The sixth 

 somite has two short crescentic ridges with the ends turned forwards 

 but not extending to the margins of the somite. The pleopods are 

 not visible. 



The telson is separated from the last somite by a distinct line of 

 articulation, and is at least a little longer than the last three somites 

 together, but the tip is not perfect in any of the specimens. At the 

 base it is about half as wide as the last somite, and it tapers gradually 

 to a slender spiniform point. The lateral margins are slightly concave, 

 and carry some short spines or teeth, but the exact number and 

 arrangement of these could not be determined, except for a group of 

 about three on each side at the base of the apical spine. The dorsal 

 surface has a strong median keel. 



The uropods are longer, probably considerably longer, than the 

 telson. Each has a short stout protopodite, produced externally into 

 a sharp tooth. The rami are very slender, and each is strengthened 

 by a longitudinal keel. The exopodite is nearly straight, and is 

 serrated on the outer, and less conspicuously on the iuner, margin. 

 The endopodite is curved inwards, and has a row of strong, widely 

 spaced spines or teeth on the inner edge, and similar but smaller 

 teeth on the distal part of the outer edge. 



Locality. — Coal-measures, Coseley, near Dudley. 



Type-specimen, No. 23 in the collection of Mr. Walter Egginton. 

 Other less perfect specimens from the same locality in the Geological 

 Department of the British Museum (I 13813, I 13814) are among 

 the paratypes. 



As regards the affinities of the species here described, it is to be 

 observed, in the first place, that the possession of a ' tail-fan ', 

 consisting of a pair of biramous appendages on either side of a median 

 telson, shows at once that it belongs to the Malacostracous Crustacea 

 and to the series Eumalacostiaca. The absence of a carapace practically 

 narrows the comparison, among the existing groups of Eumalacostraca, 

 to the Isopoda and the Syncarida. 



The expanded pleural plates of the thoracic region give Pleuroraris 

 considerable resemblance to an Isopod, and it must be admitted as 

 a possibility that they may indicate real affinity with that Order; 

 but, on the other hand, there are some important features that tell 

 against this view. Iti all receut Isopoda, with exception of the 

 aberrant family Anthuridse, the telson is coalesced with the last 

 abdominal somite, and, as this is the case also with the Tanaidacea 





