XANTHOSIA. 3 



Museum and the other in Mr. Cunnington's collection. The absence of all the parts upon 

 which generic distinctions depend has necessitated my confining myself to a description of 

 the carapace. Its nearest affinity to any recent form appears to be to the genus Mithrax, 

 and particularly to that division of the genus which is represented by Mithrax denticulatus 

 and Mithrax sculptus, both of which in form and general aspect it considerably resembles. 

 Its principal interest consists in its being another of the few examples of the occurrence of 

 a Maian form in a fossil state, the first, Mithracia libinioides, having been recorded in the 

 first part of this work. 



Family— CANCERID./E. 

 Genus — Xanthosia, Bell. 



Char. Gen. Testa multo latior quam longior, fronte lato, undulato, emarginato ; margine 

 latero-anteriore quadridentato seu quadrilobato. Orbit a distantes, magna?, rotundo-ovatae, 

 supra atque infra obscure bifissse. 



Xanthosia Gibbosa, mihi. Plate I, figs. 4 — 6. 



Margine latero-anteriore dentibus quatuor triangularibus. 



Descr. Carapace nearly twice as broad as it is long, considerably convex, the anterior 

 part granulated, the posterior punctate ; front broad, waved, emarginate, depressed in the 

 centre ; latero-anterior margin with four triangular teeth ; the anterior regions elevated, 

 particularly the proto- and meso-gastric lobes ; the nuchal furrow nearly transverse. Orbits 

 distant, large, of a rounded oval form, without teeth or other armature, the margin slightly 

 raised, and both above and beneath with two very small, indistinct fissures. 



Length of carapace, 07 inch; breadth, 1*2 inch. 



Three specimens are in Mr. Cunnington's collection, from the upper Greensand of 

 Wiltshire. 



Obs. In its general aspect this species so much resembles many of the genus Xantho, and 

 especially that section of it which is represented by Xantho florida of our coasts, that at first 

 sight I thought it might be considered as belonging to that genus. Notwithstanding, how- 

 ever, the absence, in all the specimens observed, of most of the parts on which generic cha- 

 racters depend, the greater breadth of the carapace in proportion to its length, the greater 

 distance of the orbits from each other, their larger size and more simple structure, the greater 



