GEOLOGICAL SURVEY OF THE TERRITORIES. 403 



Inches. 



Proximal caudal, length 2. 14 



Proximal do., width cnp . .' 3. 43 



Proximal do., depth cup 3. 23 



Caudal without diap., No. 1, length 1. 6 



Caudal without diap., No. 1, depth cup '.. 2. 65 



Caudal without diap., No. 1, width cup 2. 6 



Caudal without diap., No. 1, height neural canal 4 



Caudal without diap., No. 1, antero-posterior width neural spine 8 



Caudal without diap., No. 2, length 1.2 



Caudal without diap., No. 2, depth cup 2. 15 



Caudal without diap., No. 2, width cup 1. 86 



Caudal without diap., No. 2, width neural sp. (antero-posterior) 1. 07 



Caudal without diap., distal, length 5 



Caudal without diap., depth cup 85 



Caudal without diap., width cup 64 



Caudal without diap., distal ; diameter, antero-posterior, of neural spine 40 



The points of attachment of the chevron bones on the distal vertebrae 

 are strongly-marked pits ; on the anterior, the anterior margins of the 

 pits are raised and continuous with the chevrons. 



The muzzle presents the usual characters of the large Mosasauroids, 

 but adds a peculiarity in the prolongation of the premaxillary boce into 

 a cylindric mass forming an obtuse beak beyond the premaxillary teeth. 

 The bone is narrowed anteriorly, and does not descend regularly as in 

 Mosasaurus sp., but continues to its abrupt and narrow termination de- 

 scribed. The extremity is deeper than wide. Immediately in front of 

 and between the anterior premaxillary teeth, a short acuminate projec- 

 tion interrupts the surface, and in front of this, a transverse depression. 

 Above, the surface becomes flattened, and presents two shallow longi- 

 tudinal depressions continuous with the nostrils. Where the premax- 

 illary rather suddenly contracts into its spine, it is materially wider than 

 the maxillary on each side of it ; in M. missuriensis it is narrower, accord- 

 ing to Goldfuss. The maxillary border of the nares is rather suddenly 

 concave at the anterior extremity of the nares, narrowing the maxillaries; 

 the latter gradually widen by the expansion of their inner margins. 



No part of the frontals is preserved, but a considerable part of the 

 pre-frontal remains. It unites by a very coarse overlapping suture with 

 the maxillary, whose outline forms an irregular chevron with the apex 

 pointing forwards in the middle of the maxillary bone. This, it will be 

 seen, is very different from the form given by Goldfuss in the M. missuri- 

 ensis, where the most anterior point of the suture is on the nareal mar- 

 gin. The external margin of the bone behind is contracted considerably 

 within the maxillary border, previous to its outward extension toward 

 the orbit. This is much less marked in the Glidastes projpython, but is 

 distinct in II. missuriensis. 



The maxillo-premaxillary suture gradually descends to the alveolar 

 border to the extremity of the maxillary bone, where it descends abruptly, 

 forming an interlocking suture quite different from that squamosal type 

 already observed in other species of the order. The length of the pre- 

 maxillary anterior to this point is three-fourths the length of the same 

 to the beginning of the nares. 



The number of teeth on the maxillary bone was probably thirteen ; 

 twelve alveolae and bases remain, and one is added in the position of the 

 posterior of M. missuriensis, if such existed ; this may be questioned 

 in consideration of the small number of mandibular teeth. Premaxillary 

 teeth two on each side, the anterior with bases separated only by a 

 groove. Throughout the whole series the bases of the teeth are con- 

 siderably more exposed on the inner than the outer side. 



The crowns are everywhere sub-cylindric at the base, the inner face 



