212 MR. SCLATER ON BIRDS FROM BRITISH GUIANA. [Feb. 1, 



a few suggestions as to the affinities of the orders of Mammalia indi- 

 cated by the structure of the placenta. We clearly, of course, have to 

 start with forms which could not be grouped with any of the existing 

 orders, but which might be called the Protoplacentalia. They pro- 

 bably had the primitive type of placenta described above : the 

 nearest living representatives of the group are the Rodentia, Insec- 

 tivora, and Cheiroptera. Before, however, these three groups had 

 become distinctly differentiated, there must have branched off from 

 the primitive stock the ancestors of the Lemuridse, the Ungulata, 

 and the Edentata. 



It is obvious on general anatomical grounds that the Monkeys 

 and Man are to be derived from a primitive Lemurian type ; and 

 with this conclusion the form of the placenta completely tallies. The 

 primitive Edentata and Ungulata had no doubt a diffused placenta 

 which was probably not very different from that of the primitive 

 Lemurs ; but how far these groups arose quite independently from 

 the primitive stock, or whether they may have had a nearer common 

 ancestor, cannot be decided from the structure of the placenta. The 

 Carnivora were certainly an offshoot from the primitive placental type 

 which was quite independent of the three groups just mentioned; 

 but the character of the placenta of the Caruivora does not indicate 

 at what stage in the evolution of the placental Mammalia a primitive 

 type of Carnivora was first differentiated. 



No important light is thrown by the placenta on the affinities of 

 the Proboscidea, the Cetacea, or the Sirenia ; but the character of 

 the placenta in the latter group favours the view of their being 

 related to the Ungulata. 



2. On some Birds collected by Mr. E. F. im Thumin British 

 Guiana. By P. L. Sclater, M.A., Ph.D., F.R.S., 



Secretary to the Society. 



[Received January 17, 1881.] 



Mr. Everard F. im Thurn having placed in my hands for deter- 

 mination a series of bird-skins collected by himself or under his 

 supervision in British Guiana in 1878 and 1879, I have had great 

 pleasure in putting names to these specimens. Amongst the 

 160 species, examples of which are in the collection, are some 

 which require a few remarks for their better identification. These 

 are: — 



1. ViREOLANITJS LEUCOTIS (Sw.). 



Vireolanius leucotis, Salvin, Ibis, 1878, p. 443, pi. xi. 

 One example, obtained in June 1879 on the Mazaruni river by H. 

 Pauli, a collector employed by Mr. im Thurn. 



The acquisition of this specimen is very satisfactory, as it enables 



