254 S. W. WILLISTON NEW GENERA OF PERMIAN VERTEBRATES 



this transverse rugosity, and between the slightly elevated lateral margins. 

 is flat or gently concave. 



On the sides posteriorly there is a large cavity, with an angnlated slit- 

 like opening at its bottom, forming a false temporal fenestra, which 

 doubtless is merely a greatly enlarged and closed otic notch.^ It is 

 bounded above by the heavy overhanging lateral border of the cranial 

 table. The epiotic angles, produced into long horns, instead of ending 

 freely, as in other Stegocephala, turn directly downward to fuse with the 

 quadrate below, inclosing what would otherwise be a simple notch into 

 a large fossa and opening. Its whole exterior and outer surface is rough- 

 ened like other parts of the skull. The cavity thus inclosed extends 

 angularly at its upper anterior angle to within about 20 millimeters of 

 the middle of the hind border of the orbit and is smooth throughout, 

 i^t its bottom there is a thin, flat, angular plate, attached to the lower 

 anterior inner side of each epiotic horn, projecting upward and forward 

 to an acute angle, leaving a narrow, slitlike perforation above connected 

 with another in front reaching the lower part of the cavity, angularly 

 dilated at the upper anterior part. Close to the anterior border of this 

 plate, and near its upper angle, is the projecting end of the stapes, as 

 shown in plate 8, figure 1. The upper margin of the perforation in 

 front is formed by a narrow descending plate from the rugose upper 

 border of the cavity. The front wall of the cavity slopes backward from 

 the upper angle to a little above the quadrate articular surface ; its smooth 

 wall looks obliquely upward, baclrward, and outward. It seems probable 

 that this cavity, as thus bounded, was closed by a tympanic membrane, 

 against which the continuation of the stapes abutted. 



The precise limits of the epiotic process are not certain, but a distinct 

 line is evident on one side, indicating sutural attachment with the quad- 

 rate along the posterior side of the platelike expansion and to within a 

 short distance of the articular projection. This, I am aware, is an 

 unusual position for the quadrate, with the ear-slit or opening above and 

 in front of it, but there can be no other interpretation of the structure. 

 The quadrate is well ossified below, fused with the extremity of the ptery- 

 goid on the inner side and with the quadra to-jugal in front below. 



The occipital surface of the skull has, in the middle, a smooth, steep 

 declivity, with the small foramen magnum at the bottom, not more than 

 5 millimeters in diameter. The high rugosity of the posterior border of 

 the cranial table overhangs slightly this declivity, forming a fossa into 

 which doubtless were inserted the strong neck muscles. Just outside of 



* A closed otic notch Is not unknown among Stegocephala. See Woodward, Proceed- 

 ings of the Zoological Society, 1904, p. 170, plate xi. Gapitosaurus stantortensis Wood, 



