538 Mr. T. H. Withers on a 



a ratlier broad plate, constricted posteriorly, where it is 

 trilobed, the posterior lobe being the largest ; above the 

 second lobi; extends a sinuous groove or suture, and from this 

 to the inner anterior angle extends a longitudinal groove 

 similar to that seen in the Eocene Rhaeliiosoina and 

 Xanthopsis. 



The abdomen in specimen In. 20781 is partially preserved, 

 only the last two plates being exposed ; but in specimen 

 In. 20780 all the plates are present except the last. These 

 two specimens show that the abdomen of the male was only 

 moderately broad, and formed an acute triangle. It was 

 composed evidently of five plates — the first wide and narrow ; 

 the second not quite so wide or narrow; the next, evidently 

 representing the third, somewhat broader and not so wide; 

 next an almost square plate, probably representing the fused 

 fourth to sixth plates ; lastly, the seventh plate or telson, 

 which is subtriangular, with a somewhat narrowly rounded 

 apex. 



The sternal plates are not well exposed. In specimen 

 In. 20781 they are seen to be variously shaped, but the 

 three plates agree in having a narrowly rounded excavation 

 on the anterior margin towards the lateral extremity, which 

 is constricted and produced downwards into a small somewhat 

 triangular body. 



Chelipeds stout and their surface generally smooth. The 

 fused basis and ischium is short, rounded, and triangular. 

 Carpus short and somewhat globular, with a broad tooth at 

 the inner angle, a blunt median spine a little removed from 

 the anterior margin, and, towards the outer angle, the surface 

 produced into a boss or prominence. The merus has the 

 posterior margin very thick and rounded, but rapidly thins 

 out anteriorly and towards the articulation with the propodus, 

 and here there is a prominent spine on the ])03terior miii'gin, 

 followed below by two further equidistant spines, the lowest 

 not being nearly so large as the others. 



Chelse unequal, the major chela developed on either the 

 right or left, as shown by the fact that in In. 20780 the 

 major chela is on tiie right, while in In. 20781 the minor 

 chela is on the right, and the detached major chela 

 (In. 20782) is a left one. Tiie chelge are rather massive, 

 rounded from below to the margins, which are upturned to 

 form a ridge and consequent concavity on their inner side ; 

 there is a longitudinal ridge extending along tiie crest of the 

 palm, and on its posterior margin, both at the joint with the 

 dactylus and midway between that and the carpus, the margin 



