1910.] The Synapsid Reptiles. 115 



primitive Therocephalians (see below), by others (e. g., Broom, 1904. o, 

 Andrews, 1S96) to be an early off-shoot of the Rhynchocephaloid group. 



Procolophon, and the Pehjcosauria not ISipiapsida. 



Two other single-arched Permian orders, the Procolophonia and the 

 Pelycosauria, by many authors have been superordinally associated with one 

 or more of the above mentioned groups under the M'ell known term Thero- 

 morpha. In regard to Procolophon however Broom (1905.5) has shown that 

 wliile it is related on the one hand to the earliest Synapsida, its tarsus and 

 other characters place it rather on the side of the Diapsida. The Pelyco- 

 sauria, as revised by Case (1907) approach the Synapsida in some characters, 

 but the tarsus figured by Osborn (1907, p. 270) differs considerably from the 

 typical Synapsid type, and this, joined with other characters, indicates that 

 the group, as held by Osborn (1903) and Case (1907, p. 158), is an offshoot 

 from the base of the Diapsidan series. 



Turning now to the more generalized Synapsida we note the following 

 groups : 



Pareiasauria. 



(1) In the Pareiasauria of South Africa, as described by Seeley (1888.1), 

 the top of the skull approximates to the Stegocephalian type, especially in 

 the relations of the bones and in the absence of any fenestration. The 

 pectoral and pelvic girdles and limb bones are also of a very lowly, almost 

 Stegocephalian type. The Pareiasauria retain a cleithrum (epiclavicle) 

 and a plate-like pelvis without any thyroid ("obturator") fenestra. The 

 phalangeal formula according to Broom (1908, pp. 1050-1051) has proba- 

 bly not yet been reduced to the typical Synapsid form of 2, 3, 3, 3, 3; but 

 approaches the higher formula 2. 3. 4. 5. 3, which is characteristic of even the 

 most primitive Diapsida and which may have been inherited from Micro- 

 saurian ancestors. The Pareiasauria are shown to be Reptiles and not 

 Amphibians by the reduction of the parasphenoid and the presence of a 

 single median occipital condyle. 



(2) More or less nearly related to the Pareiasauria are the American 

 Permian family Pariotichidse of Cope, which are often referred to the Cotylo- 

 sauria. These forms have recently been redescribed by Case (1899), Broili 

 (1904) and Williston (1908). Like the Pareiasauria they resemble the 

 Stegocephalia in the arrangement of the bones of the roof of the skull and in 

 many characters of the shoulder girdle and limbs; while the base of the 

 skull is reptilian in type. A cleithrum has not yet been observed (AVilliston, 



