AND AVES OF NOKTII AMERICA. 



203 



Proximal width cup, 



" depth " 

 Caudal without diap. No. 1, length, 

 " " " " depth cup, 



" " " width " 



" height neural canal, 

 " " " antero-posterior width neural spini'. 

 Caudal do.. No. 2, length, 



" depth cup, 

 " width " 

 " " " " neural sp. (antero-posterior), 

 Caudal do., distal; length, 

 " " " depth cup, 



" " " width " 

 Caudal do., distal; diameter antero-posterior, of neural spine. 



In. 

 8.48 

 3.33 

 1.6 

 a.05 



2.0 



.4 



.8 



1.2 



2.15 



1.86 



1.07 



.5 



.85 



.(II 



.40 



The points of attachment of the chevron hones on the distal vertebras are st rongly 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 Hie large Mosasauroids, hut adds a. peculiarity in the prolongation of 

 the premaxillary bone into a, cylindric muss forming an obtuse beak beyond the premaxillary teeth. The hone is nar- 

 rowed anteriorly, and does not descend regularly as in Mosasaurus sp., 1ml continues to its abrupt and narrowed termi- 

 nation described. The extremity is deeper than wide. Immediately in front of and between I he anterior premaxillary 

 teeth, a short acuminate projection interrupts the surface, and in front of this, a transverse depression. Above, the 

 surface beoomes Battened, and presents two shallow longitudinal depressions continuous with the nostrils. Where the 

 premaxillary rather suddenly contracts into its spine, it, is materially wider than the maxillary on each side of it; in M. 

 inissiiriensis it is narrower, according to Goldfuss. The maxillary border of the nares is rather suddenly concave at the 

 anterior extremity of the nares, narrowing the mamillaries; the latter gradually widen by the expansion of their inner 

 margins. 



No part of the frontals is preserved, hut a considerable part Of the left pre-froutal 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 he seen, is very different from the form given by Goldfuss in the M. 

 inissiiriensis, where the most anterior point of the suture is on the unreal margin. The external margin of the hone 

 behind is contracted considerably within the maxillary border, previous to its outward extension towards the orbit, 



This is much less marked in the Clidasfes propyfhon, hut is distinct ill M. missuriensis. 



The maxillo-premaxillary suture gradually descends to the alveolar border to the extremity of the maxillary hone, 



where if descends abruptly, forming an interlocking suture quite different, from that, squamosa] type already observed in 



other species of the order. The length of the premaxillary anterior to this point, is three-fourths the length of the 

 same to the beginning of the nares. 



The number teeth on the maxillary bone was probably thirteen; twelve alveola' and bases remain and one is 

 added in the position of the posterior tooth of M. missuriensis, if such exisled; this may lie 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 arc considerably more exposed on I he inner than ( he 

 outer side. 



The crowns are everywhere sub-cylindric at the base, the inner fact! more convex than the outer. Posteriorly there 

 is a, posterior cutting ridge, as well as a, marked anterior one. both minutely Crenulate, but Ihe former disappears I ill in 

 the anterior teeth there is only an anterior edge, the posterior face being convex and continuous with the inner. There 



is a trace of cut ting edge on the outer portion of the extremity of the crown in the most anterior teeth, The anterior 



ridge remains very strongly marked. The surface is quite rough with longitudinal ribs, of which eight may be counted 



