GEOLOGICAL SURVEY OF THE TERRITORIES. 411 



The depressed form of the lumbar centra gives place gradually on 

 the caudals to a more elevated pentagonal outline, which is still more 

 reduced in width in more posterior regions. The haemal arches are 

 articulated and on the anterior caudals to slightly elevated bases ; on 

 the more posterior the bases are reduced in height, but more widely 

 and deeply excavated. I -have not seen the most distal caudals, and 

 hence cannot determine whether their chevron bones articulate in pits, 

 as is the case with those of L. perlatus, L. proriger, &e. On a caudal, 

 where the depth of the centrum a little exceeds the transverse diameter, 

 the cliapophysis has become narrow and thick. The excavation for the 

 neural canal is strongly marked on the more anterior caudal. The 

 smooth border of the articular ball is here narrow, and the superficial 

 nyse are fine and confined to the anterior part of the centrum. 



Measurements. 



M. 



Transverse diameter ball post-dorsal 0. 144 



Vertical diameter 097 



Vertical diameter anterior caudal , 094 



Transverse diameter anterior caudal 107 



Length centrum anterior caudal 071 



Transverse diameter neural canal 0145 



Transverse diameter basis diapophysis 032 



Transverse diameter basis diapophysis of a more distal caudal . . . 0278 

 Longitudin al diameter chevron articulation of a more distal caudal . 023 



Length centrum . - . . 068 



Depth ball centrum 093 



Width ball centrum 091 



Length centrum of a lumbar 106 



Width of articular ball 125 



In instituting a comparison between this and other known mosasau- 

 ridse it will be necessary to consider species referred to Mosasaurus, as 

 well as to liodon, from the fact that some of the former may really be 

 liodons. The liodons, with compressed or round dorsal or lumbar 

 vertebrse, may be dismissed from comparison. Of the depressed species 

 L. perlaius, Cope, is known from specimens of one-third or less the size 

 of the present one, which are further peculiar in having the diapophyses 

 of the lumbars to stand on the anterior half only of the centrum. In 

 L. ictericus, Cope, the centra are less depressed and the size still smaller 

 than in the last. 



Among Mosasauri, with depressed vertebral centra, it is to be noted 

 that none present so great a degree of depression and lateral extension, 

 except the M. brumbyi of Gibbes. They are all also much smaller. The 

 M. brumbyi was founded by Dr. Gibbes on two lumbar vertebrse from 

 the cretaceous of Alabama, which resemble those of the M. dyspelor 

 in form and also in size. It is probably its nearest ally, and may be a 

 liodon. Dr. Gibbes established the genus Amphorosteus for it, but 

 without sufficient evidence to support it. The principal point of dis- 

 tinction between it and the L. dyspelor, which I observe, is the lack 

 in the former of the strong emargination of the superior margin of 

 the articular surface for the floor of the neural canal, which is so 

 marked in the latter. I have only the figures of Gibbes to rely on for 

 this particular, and it is scarcely probable that the artist would have 

 overlooked it had it existed. Should the bounding prominences have 

 been worn off, then the restored centrum would have had a notably 



