158 BRITISH FOSSIL CRUSTACEA. 



but little is preserved, but a larger specimen (fig. 12) shows it to have been roughly 

 squamose, especially along its basal edge, the narrow squamae projecting as small spines ; 

 the rest of the surface is closely imbricated with smaller plicae. PI. xiii, fig. 14, is 

 very possibly the serrate inner lobe of this joint. The second joint (b) is large in propor- 

 tion to the rest, and widens from the base to its truncated apex. The third (i) is 

 subtriangular, the blunt apex of the triangle being anterior, and the edge articulating 

 with the next joint nearly straight or but slightly curved. The fourth joint, on the 

 contrary, is an obtuse triangle, of which the broad base is forward and moderately arched, 

 but not projecting as in the P. anglicus. It contracts rapidly behind, where it has a 

 narrow deep notch to receive the articulating process of the next joint. This (c a) is the 

 fifth, a remarkably short wide articulation, almost buried in the concave edge of the 

 great penultimate joint, and curved to follow the convex border of the triangular fourth 

 joint. It is marked by a strong transverse ridge. All these joints may be seen in fig. 

 5, but in a far less perfect state than in the fine specimen, fig. 13. The penultimate 

 joint (jy) is very large, nearly three inches long, and about half as broad. It is oblong, with 

 two rounded unequal lobes, and deeply notched at each end (the distal notch at the end 

 being the deepest), so that the joint overlaps the proximate joints at either end. The hinder 

 margin of the joint is more convex at first, then somewhat excavated, while the anterior 

 margin is straight, or nearly so ; the hinder lobes at both ends are larger than the 

 anterior ones, the proximal one, which overlaps the small fifth and fourth joints, being 

 broader and rounder, and the distal one, which abuts against the terminal palette, being 

 long and narrow. 



" The terminal joint (d) is very long, nearly three inches by nine tenths of an inch 

 wide, elongato-lanceolate, but rounded at the tip, its anterior margin a little convex and 

 plain-edged half way down, the posterior slightly concave and rather strongly serrate ; 

 the sense are shallower on the anterior margin, and deepest round the tip." 



The largest and most perfect of these organs are reproduced on PI. XXIX, fig. 2, 

 which corresponds with Mr. Salter's pi. xi, fig. 15, 'Mem. Geol. Surv.,' Mon. I, 1859. 



Body-segments. — Concerning these Mr. Salter writes — " Of the first body-ring a 

 fragment an inch and a half long and one inch wide is figured (pi. x, fig. 2). 



" It is the semicircular sweep of the outer edge of the segment, where it fits into 

 the scooped-out portion of the succeeding (second) one. The rounded margin a is 

 serrated, the serrations pointing backward. The sculpture is very minute, prominent, 

 and confined to the forward half, except a few marginal plicae on the hinder edge. All 

 are longer than wide. Fig. 2 a shows them magnified. Fig. 3 is, without much doubt, 

 the second thoracic segment. It is wider at the sides than in the middle, and turns up 

 abruptly at the forward angle to form the characteristic process. Fig. 4 appears to be a 

 larger specimen of the third ring, it has the same characters of ornamentation. In both 

 the central portion is less arched than in P. anglicus or P. arcuatus, and the sides less 

 obliquely and minutely crenulate. 



