1048 DR. R. BROOM ON THE ORIGIN [DeC. 10, 



osteology as living reptiles, but concerning tlieir origin or nearest 

 reptilian allies we have hitherto known little or nothing. 



Though Owen (2), as far back as 1845, recognised mammal-like 

 features in the Anomodont dentition, and also later Avhen he 

 described the skulls of Oynodonts and Therocephalians, Cope (3) 

 seems to have been the first to have expressed the view that the 

 mammalian resemblances found in certain Permian reptiles were 

 due to a genetic affinity. Between 1875 and 1878 the first 

 remains of Pelycosaurian reptiles were discovered, and Cope 

 recognised in them so many mammalian characters that he 

 suggested that the Mammalia had probably been descended from 

 them. As the South African Anomodonts had also a nvimber of 

 similar mammal-like characters, he united the two suborders in a 

 new order Theromorpha, a name afterwards changed to Theromora. 

 As the result of later work on the Pelycosauria.ns by Baur and 

 Case (4), and on the South African forms by Seeley and myself, 

 it became manifest that the group Theromorpha is not a natural 

 one, the Pelycosaurs being more nearly I'elated to the Rhyncho- 

 cephalians than to the mammals. Osborn (5) in 1903, in his 

 most important pajDer on the classification of the reptiles, reviewed 

 the recent work and came to the conclusion that the reptiles had 

 very early become specialised along two very distinct lines — the 

 one giving rise to the lizard -like forms and the other to the 

 mammal-like. The former group he called the Diapsida and 

 the latter the Synapsida. In the Diapsida he placed all the 

 primitive Rhynchocephaloid groups, including the Pelycosauria, 

 as well as most of those reptilian orders which seem to have 

 sprung from a Sphenodon-\i^e ancestor. In the Synapsida he 

 placed, besides the Anomodonts and " Theriodonts," the Chelo- 

 nians and Plesiosaurians. Though most recent opinion has been 

 in favour of some such division of the Reptilia, it seems doubtful 

 if the Chelonia and Plesiosauria should be placed in the Synapsida, 

 and I am inclined to agree with Boulenger (6) in placing them 

 rather with the Rhynchocephaloid groups. It seems to me, however, 

 advisable to retain Osborn's names for the two large groups, but 

 making the Synapsida only include the mammal-like forms, with 

 possibly the Pareiasauria. 



Within the last few years our knowledge of the Synapsida has 

 greatly increased. Four well-marked suborders of mammal-like 

 reptiles are recognised, viz. : the Anomodontia (Owen), for the 

 Dicynodon-like forms; the Cynodontia (Owen), for the reptiles 

 like Galesaurus and Gomphognathus with a well-developed secon- 

 dary palate ; the Therocephalia (Broom), for the mammal-like 

 reptiles, such as Scylacosaurus, which have a Rhynchocephalian 

 palate ; and the Dinocepludia (Seeley), for those specialised forms 

 which resemble Titanosuchus. For these four suborders the term 

 Therapsida has been proposed (7) as an embracing order. Pareia- 

 scmrus and its allies, such as Tapinocephcdus, Prop)appus, &c., 

 may perhaps be considered to form a second oixler of the 

 Synapsida, the Pareiasauria Seeley. 



