HOPLOPARIA. 25 



variance, however, with the fact that they are in every case unmistakeably distinct, surely 

 the reappearance of similar forms, under similar circumstances, at such remote periods, 

 without any intervening, Vmh, cannot be so explained. 



Of this genus, although, up to the present time, two species only had been found 

 belonging to an epoch earlier than that of the London Clay, I have to make known 

 four froux the Gault, and the upper and lower Greensand. The various species 

 occurring in all these beds — the London Clay, the Gault at JFolkestone, and the 

 Greensand of Lyme Regis, of Wiltshire, and of the Isle of Wight — have so many essential 

 points of structure in common, that their generic relation to each other is indisputable, 

 whilst their specific distinction is not less so ; nor are the distinctions between any two 

 species of the periods most remote from each other, of greater value or of a different kind 

 from those of the species found in the same bed ; and it is remarkable that the very cha- 

 racter upon which M'Coy founded the genus, from species in the London Clay, are essen- 

 tially identical with those which belong to all the more recently discovered species. 



Tliis peculiarity, which suggested to M'Coy the name Iloploparia, namely, the extra- 

 ordinary elongation of the supra-orbitar spine, is conspicuous also in the unusual 

 development of the rostrum, which in R. longimana is not less than half as long as the 

 carapace. 



Upon the whole, seeing that all the rocks in which these Crustaceans are. found are of 

 marine origin, we may conclude that they rather represent the recent genus Homarus, to 

 which the common lobster belongs, than Astacus, which is essentially a fluviatile genus. 



HoPLOPAKiA suLCiROSTRis, miM., Plate V, figs. 8- — 10. , 



Testa spinosa, spina supra-orbitali rostrum equante, rostro bicarinato ; digito immobili 

 manus majoris falciformi ; abdomine punctato. 



Descr. The carapace is nearly cylindrical, the anterior portion armed with several 

 rows of spines directed forwards ; a very slight furrow on the median line continued on 

 to the posterior portion ; the rostrum very long, with two sharp carinse, and a deep sulcus 

 between them ; the supra-orbitar spine as long as the rostrum, and very slender ; the 

 nuchal furrow deep, crossing the middle of the carapace in an even line ; the posterior 

 portion of the carapace minutely granulated; the abdomen smooth and polished ; the 

 epimeral plates slightly granulated; the exterior flap of the tail rounded, nearly as 

 broad as it is long ; the division of the two portions about one third from the extremity, 

 the terminal portion forming nearly a semicircle ; the anterior legs not more than twice 

 as long as the carapace, exclusive of the rostrum, the wrist and arm together about as 

 long as the hand ; the claws of very unequal size and dissimilar form, although less 

 considerably so than in H. longimana ; the larger hand about half as broad as it is 



4 



