OF THE PELYCOSAl-RIAN CENUS DIMtn-RODOX. 27 



present, sup'ratemporals and (inadrato-jugals absent. A well developed quadrate. 

 Palate a slight modification of the Rhyncocephalian type. Teeth on the pterygoids 

 in Scylacosaurus and /Elurosaurus. IMaxillary and preniaxillary differentiated as in 

 mammals into incisors, canines and molars. Occasionally more than one pair of 

 canines ; molars simple. Scapula without an acromion process ; probably a cleithrum. 

 Manus and pes unknown." Including Sctjiacosaurus, ^Elurosaurus, Ididosuchus, Deu- 

 terosaurus, Rhopalodon, TUanosuchus, and Gorgonops. 



THERIODONTIA. 



Medium sized reptiles, with temporal region supported by a single lateral arch. 

 No distinct postfrontals, supratemporals or quadrato-jugals. Quadrate rudimentary. 

 A secondary palate formed by the maxillaries and palatines. Prevomers small. 

 True vomer large. Transpalatines usually absent. Occipital condyle double. No 

 teeth in palate. Scapula with a distinct acromion. Phalangeal formula 2, 3, 3, 3, 3." 



Including Lycosaums, ? Ci/nodraco, Cynognathus, Galesaurus, Gomphognathus, 

 Microgomphodon, Triradiodon, and Diademodon. 



A glance will show the resemblance that, except for the condition of the temporal 

 arches, exists between the Therocephalia and the PeJycosauria. In Figures 7 and 8 are 

 shown the palate of Scylacosaurus and Proterosuclms drawn after Broom showing the 

 remarkable similarity of the palate in these genera to the Pelycosauria. This resem- 

 blance Dr. Broom regards as a common inheritance in the two groups from a Cotylo- 

 saurian ancestor, but it is to be observed that the genus Gorgonops is the only one in 

 which the condition of the arches is known and in this the temporal region is com- 

 pletely roofed over ; the presence of a primitively single arch in the forms otherwise 

 most closely related to the Pelycosauria is unknown from observation. Should the 

 genera, Scylacosaurus, Proterosuchus, JLlurosaurus or any of them prove to have an 

 arrangement of the temporal bones indicating the Rhyncocephalian type, even though 

 the temporal vacuities are very poorly developed or even not open the extremely 

 primitive origin of the single arched ancestor of the mammalia as assumed in Osborn's 

 Synapsida and Diapsida must be subject to some revision. 



Slate Normal School, 

 Milwaukee, Wis. 



