[lam be] 



CRETACEOUS GENUS STEGOCERAS 



25 



either side is a vaulted space in the roof of which, leading to the upper 

 surface, is the supratemporal fossa. 



The cranial elements wholly or partially preserved, or indicated 

 are determined as follows: — 



Parietals and frontals, coalesced and forming an axial mass, 

 most thickened and elevated in front of its posterior one-third of 

 length. 



Sq.uamosals, constituting the overhanging postero-lateral angles 

 of the head, bounding the parietals externally, and forming the 

 greater part of the posterior border. 



Postorbitals, external to the parieto-frontal mass in advance of 

 the squamosals, and continuing forward the overhanging lateral 

 border. 



Postfrontals, external to the parieto-frontal mass, bounding the 

 postorbitals in front, continuing the lateral border forward. 

 Exoccipitals, meeting above the foramen magnum. 

 Supra-occipital, arching back from the junction of the exoccipitals. 

 Otic mass, alisphenoids, orhitosphenoids, and presphenoid forming 

 the side-walls of the brain-case in advance of the exoccipitals. 

 ? Parasphenoid. 



The coalescence of the parietals 

 appears to have been complete in all cases. 

 In most of the specimens no trace is dis- 

 cernible, in the upper surface, of the inter- 

 frontal and parieto-frontal sutures, but in 

 one specimen, collected in 1917 (text 

 figure), the frontals have separated from 

 each other and from the coalesced parietals 

 revealing to their full depth and extent the 

 interfrontal and parieto-frontal suturai 

 facets; the same sutures are seen in a less 

 perfect specimen Cat. No. 2369; also in 

 the type of Stegoceras validus what appears 

 to be an indication of the parieto-frontal 

 suture was observed in the upper surface. 

 In the lower surface, however, of all the 

 specimens, the parieto-frontal suturai line 

 is preserved, usually with distinctness, 

 crossing the roof of the brain-cavity, and a longitudinal line toward 

 the front generally marks the union of the frontals. The limits of the 

 supra-occipital bone have not been fully determined. The periotics 

 (or otic complex), the alisphenoids and the orbitosphenoids are 



Parieto-frontal mass, 

 specimen No. 2379, 

 superior aspect, show- 

 ing the interfrontal 

 and parieto-frontal 

 sutures, 4/ 10 nat. size. 



