4: DESCEIPTION OF A SKULL OF 



strongly developed sagittal crest and temporal fossa that the zygomatic arch in Mega- 

 lonyx may, not unlikely, prove to be completely closed. Our specimen shows that 

 he was correct in his conclusion. I will here give a detailed description of this 

 structure. 



The zygomatic arch. — The zygomatic process of the squamosal bone projects 

 outward and forward, as in M. jeffersoni. Its upper border descends first in a concave 

 curve for about 8 cm. from the inion (thereby differing from M. jeffersoni, in which the 

 cori'esponding line is strongly convex, Leidy, Z.c, PI. I) ; along the following 4 cm. it 

 deviates less from a horizontal direction ; and, finally, in its last 4 cm., it rises gently 

 upward to meet the border of the malar bone, about 15 cm. from its origo on the 

 border of the inion. 



The glenoid fossa is curved outward and forward, measuring 5 cm. in length and 

 2.5 cm. in greatest width. There is but a rudimentary postglenoidal process, but the 

 antero-exterior margin of the fossa is expanded into a horizontally flattened exglen- 

 oidal process. The inferior border of the bone extends 4 cm. in advance of this pro- 

 cess, and there meets the postero-inferior process of the malar bone. The space 

 between these two processes is more or less roughened. 



The external surface of the zygomatic process, viewed from above, is sigmoid ; 

 but between its upper and lower margins it is more or less concave throughout. Its 

 least vertical diameter is 32 mm. 



The anterior end of the zygomatic process slants upward and forward with a 

 gentle curve and finally makes a sudden turn U2:)ward and backward. The corre- 

 sponding emargination in the malar bone does not describe a similar curve, but 

 passes, in its upper poi-tion, with a beveled edge, behind (inside of) the edge of the 

 zygomatic process. The sutures are entirely obliterated in the arch of the right side, 

 but the left arch has been fractured accidentally, and the suture cracked open. 

 However, even on the right side (PI. I) the location of this suture may be seen as a 

 line, from both sides of which the faces of the two bones slope in different directions. 



There is a rough semicircular ridge on the inside of the zygomatic process, pass- 

 ing from its infero-anterior point to a point perpendicularly above the same. In front 

 of this ridge is a broad shallow fossa extending over a considerable portion of the 

 malar bone. 



Leidy's description of the malar ].)rocess of the maxilla in M. jeffersoni {I.e., p. 9) 

 applies also lo M. leidyi, except in the latter having the infra-orbital canals double, 

 a horizontal septum dividing each into two canals, one immediately above the other. 

 This individual presents, also, an asymmetry in these canals, for, whilst that of the 

 right side has but a rudimentary septum forming a complete partition only for a short 



