100 



spheual roof is sepai'ated on each side from the zygapophyses by an acute 

 groove gives the former a distinctness more apparent than real. 



The fixed hypapophyses are short and broad. The centra are not elon- 

 gate. Those of the anterior dorsals present an obtuse keel below. 



Measurements. 



M. 



Length of a median cervical 0.043 



Diameter of the ball of a median cervical, vertical 0. 0^9 



Diameter of the ball of a median cervical, transverse 0. 033 



Length of the anterior dorsal 0. 042 



Width of the cup 0.032 



Found by the author on a low bluff, or "break," on Butte Creek, four- 

 teen miles south of Fort Wallace. 



A second specimen of this saurian has since been discovered by Profes- 

 sor Mudge. The frontal bone is thick, and presents a median keel. The 

 quadrate is flat on the posterior inner face, so that the stapedial pit is exca- 

 vated in a plane surface ; the internal proximal angle is nearly right. The 

 vertebns are small, and the hypapophyses short, and with horizontally trun- 

 cate articular faces, as in the type-specimen. 



This species is the smallest known Platecarpus. 



LIODON, Owen. 



Vertebrae without zygospheual articulation, and with very weak zyga- 

 pophyses ; the chevron-bones not coossified to the centra. Teeth with 

 opposite acute edges, compressed, lenticular in section. Humerus small, 

 narrow. 



The quadrate bone in the known species of this genus is of small pro- 

 portions, and presents a very prominent internal proximal angle and longitud- 

 inal ridge. The structure of the cranial bones is light. The zygapophyses 

 are weaker, and disappear more anteriorly than in any other genus, approach- 

 ing nearest to Mosasaurus in this respect. 



There are four species of the genus known from the Kansas chalk, all 

 of which have the end of the premaxillary bone protuberant and truncate. A 

 species of similar character has been described by Mr. Hector, from the Cre- 

 taceous of New Zealand. Three species from the greensand of New Jersey 

 arc similar in many respects; but the forms of their muzzles are unknown. 



The typical species of this genus (Liorton anceps, Owen) is very little 

 known, but few remains having so far been obtained from the English chalk, 



