No. 434] THE AMERICAN PELYCOS A LRI A. 



97 



In Cynognathus the palate is typical reptilian, the teeth have 

 only small lateral tubercles and the whole dentition resembles 

 that of Dimetrodon in the large incisors and canine, the sharp 

 diastema and the convex tooth line. 



In Galesaurus and in Cynognathus platyceps there is a 

 single temporal arch with no trace of an inferior temporal 

 vacuity. The bar is formed of two parallel bars, one above the 

 other, with no indication of distinct bones forming each bar. 

 The lower of these bars is called by Lydekker ( Lydekker '90) 

 the quadrato-maxillary and the upper the squamoso-maxillary ; if 

 the condition of this form is derived from a condition represented 

 by Cynognathus crateronotus the lower bar is really the jugal, 

 the quadrat o-jugal having disappeared beneath the psq + sq and 

 the upper bar is the prosquamosal + postorbital. As the prosqua- 

 mosal is already united with the squamosal, there is now a single 

 mass, the postorbital -f prosquamosal + squamosal. Seeley points 

 out that in Galesaurus the lower portion of the psq + sq descends 

 below the quadrate posteriorly. 



In Galesaurus the palate approaches the mammalian condition 

 found in the ( iomphodontia and the teeth have strong lateral 

 tubercles. The diastema has almost entirely disappeared though 

 there is still a prominent canine. 



In Gomphognathus the temporal region is much the same as 

 in Cynognathus, the region is described as follows by Seeley 

 (Seeley '95) "the squamosal rest upon the parietal as a thin film, 

 which descends laterally to the level of the occipital condyles, 

 when it makes a sudden angular bend upward and outward. 



The lateral contour of the ascending bar of the squamosal 

 bone is convex, and nearly at right angles to that of the lateral 

 border of the occiput; both are equally thin, and the two plates 

 define a V-shaped squamosal notch which is open superiorly. 

 But the squamosal bone is much more massive than is at first 

 obvious, and below this thin external posterior plate, there is an 

 excavation in the bone, which shows it to be expanded laterally 

 for 1 % inch beyond the compressed ridge at the base of the V- 

 shaped fold just described." 



The squamosal described by Seeley is of course the psq + sq of 

 this article ; the prosquamosal portion forms the posterior part of 



