262 Bulletin American Museum of Natural History. [Vol. XII, 



noms generique de Dactylomys et de Nelomys (/. c., p. 51). He 

 here restricts the name Echimys " aux especes analogues par leur 

 organization a 1' Echimys setosus" (I. c., p. 30). As, however, 

 the type of Echimys should be one of the two species originally 

 referred to it, the type is properly E. spinosus Desm., unfortu- 

 nately a species not strictly congeneric with E. setosus Desrn., 

 now referred to the genus Mesomys Wagner (1845). 



Mesomys was originally based 1 on a tailless specimen from 

 Borba, Brazil, which was also the basis of the type species, 

 Mesomys ecaudatus (sp. nov. ex Natterer MS.). The genus is 

 here characterized as follows : " Habitus Loncherium, dentes 

 Echinomyum, spinae validae, cauda nulla" ; and he adds : " Die 

 einzige mir bekannte Art ist Mesomys ecaudatus Natt." Quoting 

 later from Natterer's manuscript notes, he says the specimen was 

 a pregnant female, and though the young were still very small, 

 they had short tails. 2 This shows that the tailless condition of the 

 type of Mesomys, was only the frequent abnormality common to the 

 various species of South American Spiny Rats. 3 Winge and 

 Trouessart associate with this species E. spinosus Desm., as well 

 as certain other species, but I find no satisfactory account of the 

 dentition of M. ecaudatus. In any case, the type of Echimys is 

 E. spinosus Desm. Therefore the large group of species now 

 currently referred to Echimys, namely the E. cayennensis group, 

 is still in need of a name, since Dactylomys I. Geoffroy (1838), 

 Isothrix Wagner (1845), Lasiuromys Deville (1852), Thrinacodus 

 Giinther (1879), Thricomys Trouessart (1880), and Kannabateo- 

 mys Jentink (1891), are all so different from the present group as 

 not to require consideration in this connection. Nelomys Jour- 

 dan (1837) and Phyllomys Lund (1841) are both, apparently, syno- 

 nyms of Loncheres. 



The foregoing may be summarized as follows : 

 i. The name Echimys was given to a genus of mammals by 

 Etienne Geoffroy Saint-Hilaire in 1808 or 1809, in a work still 

 unpublished. 



2. Echimys as the name for a genus of mammals was first pub- 

 lished by F. Cuvier in 1809, from a manuscript work by E. 



1 Arch. f. Naturg., 1845, i, 145. 



2 Abhandl. der II Cl. d. k. Akad. d. Wiss. Munchen, V, Abthl. 2, 1848, aq?. 



3 On this condition in Echimys trinitatis see Allen and Chapman, Bull. Am. Mus. Nat. 

 Hist., V, 1893, 226. 



