16 FOSSIL MALACOSTRACOUS CRUSTACEA. 



in both sexes as in the former species, excepting that in the female the sixth and seventh 

 segments are larger in proportion. 



Length of carapace, VS inch; Lrcadth, 2-5 inch; Height, 06 inch; thickness of the 

 animal, 11 inch. 



Ods. The distinctions between this and the former species consist rather in the 

 proportion of the various parts, than in any strongly marked exclusive characters. It 

 is wider and flatter in proportion ; the height, taken from a horizontal line extending from 

 the posterior margin to tlic front, being only one thu'd of the length, whilst in X. Leachii 

 it is nearly half. The whole of the tubercles are much less prominent, the carapace less 

 convex — the front being nearly horizontal ; the puncta of the carapace are larger, and 

 almost as conspicuous towards the front and in the grooves between the tubercles as 

 in the other parts, and there are scarcely any perceptible granulations on the interspaces 

 between them. The difference in the number of tubercles on the crest of the hand 

 referred to by Professor M'Coy, is more apparent than real, arising only from the union 

 of the two anterior ones. The tubercles on the outer face of the hand are exactly 

 similar to those of X. Leachii. 



It is found Avith the former species in the Island of Sheppey, at Southend, and in 

 the northeiTi suburbs of London, from Avhich localities there are several specimens in 

 the collections of !Mr. Bowerbank, Mr. Wetherell, in my omi, in that of the University 

 of Cambridge, and in the British Museum. 



Xantuopsis unispinosa, M'Coy. Plate II, fig. 1. 



Testa, sexta parte tantum latiore quain longiore, seque convexa, tuberculis regioniun 

 fere obsoletis. 



Xanthopsis unispinosa, M'Coy. Ann. Nat. Hist., 18-19, p. 164. 



Descr. The carapace in this species is not more than one sixth broader than it is long ; 

 almost uniformly convex from front to l)ack, and not much less so from side to side; 

 the puncta on the surface more distant than in X. Leachii ; the tubercles of the different 

 regions very depressed or almost obsolete, though occupying the same places as in 

 the other species ; the posterior lateral process short, flattened, triangular, and sharp 

 pointed ; the penultimate one smaller, and the two anterior obsolete. 



It is distinguished from A". Leachii by the less degree of deflexion of the front, 

 by the very shght elevation of tlic tubercles on the posterior region, by the character 

 of the lateral processes, and the more coarse punctation of the smface; and from 

 X bispinosa by the relative proportions of the length and breadth of the carapace, 

 and by its more considerable and regular convexity. 



After careful consideration, and the examination of several specimens, I have come 



