151 



sis with stout inferior horizontal branch, which is capped by an extension of 

 the articular cartilage from the rim of the cup. Occipital crest elevated, sub- 

 vertical. Quadrate broad below ; pit sunk between bounding ridges. 



Description. — There is a great disproportion in the sizes -of the cervical 

 and posterior dorsal vertebrae ; the centra of the latter are rather more de- 

 pressed than those of the former. They are similar in proportions to those 

 of the other Platecarpi, and shorter than those of the Clidastes. The short 

 axes of the articular faces are subvertical. The rudiment of zygosphen is 

 seen in the slight anterior prolongation of the roof of the neural canal. The 

 keel of the hypapophysis of the atlas is short and obtuse. 



The greater part of the cranium is preserved. The supraoccipital keel is 

 vertical, and furnished at the summit with a plicate knob for the insertion of a 

 ligamentum nucha. The thickness of the walls of the bone is not equal to that 

 in H. coryphceus, and the suture for the parietal is a double scpiamosal ; i. e., 

 with a groove along the middle of the edge. The basisphenoid is but slightly 

 keeled below, and is distally expanded into a horizontal plate on each side. 

 The parietals are, as usual, confluent, and send off two light arches postero- 

 laterally for union with the squamosal bone. Between their origins are two 

 subparallel ridges, which disappear, the transverse section of the narrow part 

 of the parietals being rounded. The lateral ridges within the temporal fossse 

 are obsolete, while the convergent angles which bound the parietal table pos- 

 teriorly are strongly marked. This table is nearly plane, and the foramen 

 parietale is large. The frontal is narrowed in front, and has an elevated keel 

 along its anterior half. The olfactory groove is not much contracted behind, 

 but is closed by the apex of the rugose area in front of the foramen parietale. 



The palatine bone is narrow, and the external margin is very slight, the 

 bases of the teeth being exposed in that direction. The inner margin is 

 much thickened downward, but not so as to be a vertical plate. The hinder 

 part of the bone is flat and horizontal, with a long maxillary process. The 

 pterygoid notch falls opposite the second tooth from behind. The whole 

 number of teeth is eleven. 



The jaws are represented by the greater part of all of the tooth-bearing 

 portions. The maxillary bone is shallowly sulcate on the exterior face. Its 

 proportions are quite similar to those of the H. coryphceus, but the teeth it 

 supports are larger and fewer. There are none missing from the extremities 

 of the specimen, the whole number being ten ;, in the H. corypha;its, there are 



