6 FOSSIL MALACOSTRACOUS CRUSTACEA. 



The history of the name which has been given to this genus is somewhat cnrious. On 

 obtaining specimens of several species of Crustacea from the Gault, Mantell applied to Dr. 

 Leach, as the iiighcst authority on the subject, for information respecting their atiiuitics. 

 Li the present case the naturalist, misled by a superficial resemblance, gave his inquirer 

 the name of Etims, a well-known recent genus ; and as caligraphy was not one of my 

 distinguished friend's qualifications, Mantell doubtless read the word Et/ju><, published it as 

 on Leach's authority in two, at least, of his works, and Efi/us it became. I hesitated 

 whether it was desirable to perpetviate a name which was only not erroneous because it 

 was a blunder, but on consideration it ap[)eared that it would be inconvenient to change 

 a generic term which had l)ecome sanctioned by long use and frequent repetition. 



This anuising mistake in nomenclature is, however, not the most important error 

 which has occurred in relation to this species. On examining the collection of Gault 

 and Greensand Crustacea at the Museum of Practical Geology, I was struck with the 

 number of specimens which were marked Eeiima (jranom of M'Coy, the whole of wiiich, 

 including some from Candn'idge, I found were specimens, more or less worn, of Elyun 

 Martini. This circumstance led me to investigate more closely the description given by 

 that author of the genus Beussia and of the species //raiiosa, and I soon became perfectly 

 satisfied that this genus has been founded upon a few worn specimens of the present 

 species, and must, therefore, be reduced to a mere synonym. If it were wished to 

 select an example of the extreme dissimilarity between diflcrent representations of the 

 same subject, which so often occasions trouble and mistake to naturalists, and not un- 

 frcquently leads to glaring errors, it would be scarcely possible to select one more 

 striking than is afforded by a comparison of the wretched woodcut in Mantell's ' Medals ' 

 of Elyus Mfirlini, with the engraving of M'Coy's Itcussia yranosa in his ' Contributions 

 to Palaeontology.' Nothing short of a critical examination of the specimens themselves 

 could lead any one to suppose their identity. 



There is in Mr. Carter's collection a fragment of a carapace which ditlers in some 

 respects from the normal form of E. .Martini. The latero-antcrior margin has four lobes, 

 which are not furnished with the sharp tubercles which are usually observed on this part. 

 There are, however, similar tubercles on the anterior portion of the carapace, the distri- 

 bution of which differs somewhat from their ordinary arrangement. 



I give a figure of the specimen in Plate I, fig. 1 2. 



GemiH — DiAULAx, Bell. 



Species unica. Diaulax Carteriana, mihi. Plate I, figs. 14 — 16. 



Descr. Carapace very minutely and uniformly granulated, somewhat broader than it 

 is long, its greatest breadth immediately in front of the nuchal furrow ; very convex from 



