806 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



are sieeu, as in L. aquilunguisandL. Incrassattis, in the dentary bone on the 

 inner side of the roots of the functional teeth. As these develop, they ap- 

 pear to take position immediately below the crown of the old tooth, and 

 grow vertically in its axis, finally displacing the latter in the manner so 

 characteristic of the Crocodilia. 



The dentary bone is not deep, bat is robust in the transverse direction. 

 The external side is little convex in the vertical direction, and displays a 

 smooth surface. A series of rather large foramina, rather closely 

 placed, extends near the superior alveolar margin. The inner face of 

 the dentary is divided into two subequal planes by a wide, open, longi- 

 tudinal groove, which terminates at the posterior border of the symphysis. 

 The surface is smooth. The symphysis is a short plane, oblique to the 

 long axis of the dentary bone, and having the usual antero-superior 

 oblique direction. It is short, and is characterized by its absolute 

 smoothness. Near its anterior inner border, there is a large foramen. 



This reptile differs from the L. incrassatiis from the Judith Eiver beds 

 of Montana in many respects : — (1) There is no tooth having the form of 

 the canine of that species, i. e., having the transverse greater than the 

 longitudinal diameter, and the cutting edges opposite ; (2) the anterior 

 edge is not carried to the middle of the inner side of the crown in the 

 anterior tooth i^reserved; as to the ramus, (3) the groove of the inner 

 side is much inferior in position in the Colorado animal ; (4) there are 

 no symphyseal rugosities, as in L. incrassatus.; (5) the ramus is shallower 

 and thicker. 



The species may then be named Lcda})^ triJiedrodon, from the form of 

 the second tooth.- 



Measurements. 



M. 



Depth of ramus at posterior extremity of symphysis 0.090 



Width of ramus at the same point 0.050 



Depth of ramus at sixth tooth 0.095 



V^idth of ramus at sixth tooth , 0.045 



Depth of ramus at sixth tooth to the internal groove 0.050 



Length of portion of ramus supporting nine teeth 0.260 



TT,. , , , „ rr XI i. XI ^transverse 0.015 



Diameter of base of crown of fourth tooth s , , . n noo 



( antero-posterior 0.022 



Total length of third tooth 0.145 



-TV- . f. c -c XI • 1 X ,,< transverse 0.021 



Diameter of base of crown of third tooth < ^ . . n no-. 



( antero-posterior 0.022 



Width of anterior (convex) face 0.017 



Length of crown of second tooth 0.045 



Width of inner face 0.019 



Width of exterior face ' 0.020 



Width of anterior face 0.012 



In this connection, I may mention that Prof. O. 0. Marsh, of Kew 

 Haven, has recently created another synonym by renaming the genus 

 Lidaiis. This is done on the supposition that the latter name is pre- 

 occupied in entomology. The name has been used in that science, it is 

 true, but simply as a synonym, and was therefore not employed or occu- 

 pied when I applied it to this genus of extiuct reptiles. 



