Hatcher : Li iit.K Known Fossil Vkriehrai-ks. 133 



The presence of a fourth cone on P.-'', together with the tendency 

 to division exhibited by the internal cones of MJ- and M.^, at once 

 distinguish this species from Z. gi-aci/is of Marsh. By some these 

 characters might be considered of generic importance, but I have pre- 

 ferred to treat them as of only specific value. 



A diastema exists in front of P.'"*, but the bone is broken away a 

 little in front of that tooth. The infraorbital foramen is situated 

 above and slightly in advance of the anterior border of P.-"^. A crown 

 view of the type specimen is shown in Plate I, Fig. 3, while Fig. 4 is 

 a reproduction of Marsh's type of L. gracilis. 



I have selected No. 103 as a collateral type of the present species, 

 since it agrees in size and was found in the same locality with the type. 

 It consists of a portion of aright ramus with P.^ and M.y, ^, -^ in posi- 

 tion and the alveoles of P.^. It is about one third smaller than Leidy's 

 type of Z. spectabilis, while agreeing very well in size and tooth struc- 

 ture with the lower jaw of Marsh's type of Z. gracilis, though differing 

 from the latter in wanting the deep groove on the inner side of the jaw, 

 which, according to Marsh, extends from the dental foramen nearly to 

 the symphysis. In the present specimen P.^ is the larger tooth of the 

 series. It is subtrenchant and supports a principal median cone with 

 a small tubercle on the narrow anterior border, while expanding pos- 

 teriorly to form a broad heel with low external and internal cones. 

 Molars y and ^ are quadrangular in outline, with crowns supporting 

 four cusps, two anterior and two posterior, each pair connected by 

 transverse ridges, while in addition an oblique ridge joins the antero- 

 internal cone v/ith the posteroexternal cone of each true molar, a 

 character not shown in Marsh's figures of Z. gracilis. In addition to 

 the four cones and three crests already described, there is in M.-j a 

 third posterior lobe bearing a fifth cone situated behind and inter- 

 mediate to the posterior paired cones. 



The ramus is proportionately quite strong and increases in depth 



anteroposteriorly. There is a small foramen on its external surface 



between P. g- and y, about midway between the superior and inferior 



borders. 



Measurements of the Type (No. 100). 



M. 



Length of superior true molar series .... 013 



" " M.' 005 



" " M.? 004 



" " M.' 0035 



" " P.i 0042 



" " P.3 007 



