A DESCRIPTION OF THE GENUS DIMETRODON, COPE. 25 



structure, of which the shorter limb is inferior, extending to the jugal, while the longer 

 limb is posterior, extending to the supratemporal [prosquamosal], in contact with the 

 parietal. It encloses no foramen with the latter ; but it encloses a larger foramen with 

 the jugal, zygomatic [quadratojugal] and supratemporal [prosquamosal] at the other 

 boundaries. This is the infratemporal foramen of Baur. Posterior to the parietal is a 

 small transverse element, which appears to be merely adherent to the former. Its 

 determination is not easy at present. The supratemporal [prosquamosal] is elongate 

 vertically, and narrow antero-posteriorly. Beneath and towards the middle line of the 

 skull is a part of another bone which may be the paroccipital, or even exoccipital. The 

 pineal foramen is distinct. No parietoquadrate arch." 



" In Clepsydrops the structure is apparently the same, although the form is much 

 less modified. The quadrate articulation is nearly in line with the maxillary dental 

 series (Fig. 6, PI. II), and the jugal is nearly horizontal ; its inferior border being con- 

 cave upwards. No bar extends posteriorly from the postorbital, which joins the supra- 

 temporal [prosquamosal], enclosing with it the infratemporal foramen. No indication of 

 a supratemporal foramen can be found in the rather mutilated specimen. I think it was 

 not present." 



"In Edaphosaurus Cope (Fig. 5, PL II), the skull is of a more depressed type than in 

 the preceding genera. The postorbital is mainly preserved, and it is in contact with the 

 frontal proximally, and sends out no bar posteriorly. There was apparently no supra- 

 temporal foramen, but a very large infratemporal, which extended well upwards. There 

 is no parietoquadrate arch. An element, perhaps supraoccipital, terminates in a free 

 compressed apex on each side of the median posterior region. This may be homologous 

 with the small free bone described in Naosaurus, in nearly the same position. The stapes 

 is very large, and is at least partially perforated near the expanded proximal extremity. 

 It is probably fully perforated, as I have described it in the Dlopeus leptocephalus Cope." 



" In Diopeus Cope, the supratemporal is elongate in the vertical direction, and as 

 elsewhere it overlaps the quadrate at the distal extremity. Anteriorly, it sends forwards 

 a process probably for union with the postorbital bone, which is, however, entirely free 

 from the parietal, and encloses a foramen with it, precisely as in Sphenodon. It further 

 resembles the corresponding element in Sphenodon in sending upwards a branch for union 

 with the parietal. Thus there are in this genus two posterior bars and two foramina, 

 thus differing widely from the other Permian genera of this or any other country known 

 to me. Whether it has a free parietoquadrate arch I do not know, but it is probable 

 that the genus should be referred to the Rhynchocephalia, in the neighborhood of Palceo- 

 hatteria Cred. It differs from Sphenodon and resembles closely the Theriodontia in the 

 absence of an obturator foramen, and in the character of its dentition. The zygomatic 



A. P. S. — VOL. XX. D. 



