16 



POSTERIOR CRANIAL ARCHES 



temporal foramen, and that the bone which bounds it externally consists posteriorly 

 of the supratemporal bone, and not the zygomatic. Anteriorly this bone joins the 

 postorbital, postfrontal and malar. In the Transactions of the Royal Society for 

 1889, p. 244, Prof. H. G. Seeley analyzes the structure of the skull of Dicyno- 

 don, which he shows to resemble closely that of Lystrosaurus, and his analysis of the 

 posterior arch and foramen is the same as my own in the latter genus. It is evident 

 then that the Anomodonta differ from the Theriodonta in the absence of a zygo- 

 matic arch, and in the presence of a supratemporal arch, which is separated from the 

 parietal bone by a supratemporal foramen (Figs. 1-2). 



Fig. 1. Fig. 2. 



Fig. 1. Lystrosaurus frontosus Cope. Aa Anomodont from South Africa ; skull from above. Fig 2, do., from 

 right side. The lower Sq is the supratemporal. 



The South African genus Procolophon Ow. has been analyzed by Seeley* in 

 an admirable manner. The orbit is greatly enlarged, so that the region of the bars is 

 contracted. However, there is a zygomatic arch, an infratemporal foramen, and no 

 supratemporal foramen, thus agreeing with the Theriodonta, and not with the 

 Anomodonta. 



In conclusion it appears that there are four types of crania represented in the 

 Permian Reptilia, which are distinguished as follows : 



Temporal roof uninterrupted Cotylosuuria. 



A zygomatic arcli, but no distinct supratemporal or supramastoid arches Tlieriodonta. 



Zygomatic and supratemporal arches Diopeus. 



No zygomatic ; a supratemporal arch Anomodonta. 



*Philos. Trans. Roy. Soc, 1889, p. 3G9. 



