NECROCARCINUS. 19 



Family— CORYSTIVJE ? 



Genus — Necrocarcinus. 



Char. Gen. Testa suborbicularis, rostro triangulari, regionibus distinctis, tuberculis 

 raagnis instructis, margine latero-anteriore utrinque producto. Orbitce rotundae superne 

 apertae, supra bifissae. Apertura oris aeque longa ac lata, lateribus concavis. 



In the 'Memoires de la Soc. Lin. de Normandie,' of the date 1836, there occurs a 

 description, by M. Deslongchamps, of a Crustacean from our Gault and Greensand, with 

 the name Orithyia La Bechei, and in several of the late Dr. Man tell' s works * are notices 

 of the same species from the Gault, which was considered by Dr. Leach, to whom 

 Mantell referred it, as belonging to the Leucoriadae, and as nearly allied to the recent 

 genus Arcania. How our great carcinologist could have arrived at a conclusion so utterly 

 without foundation is more surprising than that Dr. Mantell should have unhesitatingly 

 adopted this hasty view, and published the species with the name Arcania BucMandii. 

 A careful examination of numerous specimens in my own collection, in that of Dr. 

 Bowerbank, and in the British Museum, has not only satisfied me that such is not its true 

 relation, but has led me rather to the opinion, not, however, without some doubt, that it 

 belongs to the Corystidae, to which family several other species found in the Gault of 

 Folkestone and in the upper Greensand of Cambridge are undoubtedly to be referred. 

 Having carefully compared the specimens of the present genus from Folkestone with those 

 from Cambridge, I find that, notwithstanding their different aspect, they are all of the 

 same species, and identical with the so-called Arcania BucMandii of Mantell ; and I have 

 had the satisfaction to find two other species of the same generic form obtained from the 

 upper Greensand of Warminster and Maiden Bradley, in Wiltshire. On searching 

 further, I discovered in a collection of fossil Crustacea from the Isle of Wight belonging 

 to Mr. Norman, of Ventnor, a large specimen of one of these species from the Chalk 

 Marl capping the firestone at Atherfield ; and I have since received from Mr. Cunnington, 

 of Devizes, several specimens of the same species from the upper Greensand of Wiltshire. 

 Several species of this genus have been found on the Continent, and I am informed by 

 M. Adolphe Milne Edwards that a Prussian naturalist has given to one of them the 

 generic name of Necrocarcinus, which I have adopted, although hitherto I have failed to 

 obtain any clue to the place of its publication. 



* ' Med. of Creat.,' p. 534 ; ' Geol. Suss.,' t. xxix, figs. 7, 8, 14 ; ' S.E. of Engl.,' p. 159, fig. 3. 



