PHLYCTISOMA. 35 



Phlyctisoma tuberculatum, mihi. Plate XI, figs. 1 — 8. 

 Testa omnino tuberculata, 



Descr. The carapace in this remarkable species is semi-cylindrical, covered in every 

 part with tubercles, which are of dissimilar sizes ; it is divided longitudinally by a narrow 

 and deep mesial sulcus, which bifurcates at the anterior part of the carapace, to enclose 

 the mesogastric lobe, which is thus completely insulated from the surrounding part of the 

 gastric region ; it is almost linear in form, terminating postei'iorly in a point at a short 

 distance from the nuchal furrow. The meso-branchial furrow is nearly parallel with the 

 nuchal, and similar to it in breadth and depth ; ' they are both rather deep, smooth, 

 and polished. There is a short, curved, connecting furrow extending between them, near 

 the margin of the carapace, separating the epibranchial lobe, and with the others enclosing 

 the mesobranchial. The cardiac region is faintly indicated, it is of a triangular form, and 

 is divided by the longitudinal mesial furrow ; the posterior margin of the carapace is 

 curved forwards, and has a distinct, raised edge, bounded by a deep furrow. The abdomen 

 is semi-cylindrical, the segments somewhat tuberculated ; the epiraeral processes are long, 

 narrow, and triangular, excepting the second, which is broad and quadrate, and hollowed 

 in the middle. The caudal segment or central plate of the tail is broad, rounded, and 

 curiously marked with sulci, ridges, and tubercles, and the margin is raised. The external 

 caudal plates are wanting in all the specimens observed. The anterior legs are robust, 

 tumid, and covered with tubercles, similar to those of the carapace. Portions of the arm, 

 •wrist, and hand are figured in the plate. The portions of ambulatory legs hitherto 

 obtained, show them to be compressed and quite smooth. 



All the known specimens, and they are very numerous, are from the Greensand of 

 Cambridge, and are principally in Mr. Carter's fine collection of Crustacea from those beds. 



Obs. This genus is in several respects a remarkable one, and presents characters which 

 forbid its being associated with any other. The general aspect of the carapace, its crowded 

 tuberculation, uniform in all its parts in the present species, the breadth and direction of 

 its sulci, give it & prima facie resemblance to Hoploparia scabra, but this similarity only 

 holds in unimportant characters, and even in these is more apparent than real. The 

 tubercles are in this species spread over the whole surface, without the mesobranchial area 

 which is so characteristic of //. scabra. The sulci also are different in their direction, 

 althougli similar in depth and in the smoothness of their surface. The most striking 

 peculiarity, however, and that by which it is distinguished from all other genera, recent or 

 fossil, which have come under my notice, is the distinct insulation of the mcto-gastric lobe, 

 which is enclosed, as it were, by a bifurcation of the longitudinal mesial furrow. The 



