1 86 Bulletin American Museum of Natural History. [Vol. XIII, 



successively removed from the Linnaean genus Didelphis as types 

 of new genera, namely D. philander, as the type of the genus 

 Philander ; JD. marmosa, as the type of the genus Marmosa ; and 

 D. opossum, as the type of the genus Metachirus ; leaving only JD. 

 marsupialis, which is claimed to be unrecognizable. As D. 

 opossum was the last recognizable species removed from the 

 genus Didelphis, this species, according to prevailing rules of 

 nomenclature, he claims must be taken as the type of Didelphis, 

 and Sarigua (Muirhead, " 1819 " ') be employed for the group of 

 species for which Didelphis has been hitherto almost universally 

 employed. It therefore seems almost as desirable to conserve 

 Linnaeus's species marsupialis as his genus Didelphis. 



It may be noted, first, that there is no doubt whatever that the 

 name marsupialis applies almost strictly to the large Opossums of 

 the virginiana type, of both North America and South America. 

 The trouble is to restrict the name satisfactorily to some one form 

 of the group of species and subspecies described since Linnaeus 

 published the name marsupialis. It is a recognized rule of 

 nomenclature that a name applied to a composite group, whether 

 specific or generic, must be conserved for some one of its com- 

 ponents when the group is later subdivided. Where a diagnosis 

 is imperfect or indecisive, as in the case of a large proportion of 

 the species of the older authors, including Linnaeus, it is neces- 

 sary, in attempting to restrict the name to some particular form 

 included in a composite group, to examine the references on 

 which the name was originally based, as well as the diagnosis, 

 the former often being of far greater importance than the latter. 



In this case Linnaeus's first reference is to the Philander of 

 Seba (" Mus. I, p. 64, t. 39 "), which is not an American animal, 

 but a species of Phalanger from Amboyna, and hence not the 

 animal called Philander from South America. 



Linnaeus's second reference is to Tyson. Dr. Tyson's first 

 memoir is entitled ' Carigueya, seu Marsupiale Americanum ; or, 

 The Anatomy of an Opossum,' published in the ' Philosophical 



1 Mr. Rehn says : " The large opossums formerly called Didelphis require a name, and the 

 oldest one available is Sarigua Muirhead, with S. virginiana as the type. The complete 

 reference is Sarigua Muirhead, Brewster's Amer, Edition Edinburgh Encyclopedia, Vol. 

 XII, Part II, p. 505, 1819." 



This reference, however, is erroneous as to date, and misleading as to the title of the work 

 cited. The correct citation would be Brewster's Edinburgh Encyclopaedia, Amer. Ed., Vol. 

 XII., Pt. 2, p. 505, 1832. The important error is in the date, which is 1832 instead of 1819. 

 The reference to the original edition, where the matter is the same, is Brewster's Edinburgh 

 Encyclopaedia, Vol. XIII, p. 429, 1830 the date being in this case 1830 instead of 1832. 



