286 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



The three inferior molar teeth, mi-ma, measure 

 longitudinally 41 millimeters, as compared with 42 in 

 the type of L. popoagicum. The external crescents 

 (protoconid, hypoconid), the internal cones (meta- 

 conid, distinct metastylid, entoconid), and the cres- 

 centic third lobe of ms (hypoconulid) are characteristic. 



Lambdotherium priscum Osborn 



Text figures 146, 234, 235, 238-240 

 [ For original description and type references see p. 194] 



Type locality and geologic horizon. — Wind River 

 Basin, 3 miles east of Lost Cabin, Wyo.; Lambdoihe- 



FiGURE 238. — Front part of type lower jaw of 



Lambdoiherium priscum 

 Natural size. Am. Mus. 12822, reversed, showing the long postcanine 



diastema, the three lower premolars, and the first lower molar. 



Locality, 3 miles east of Lost Cabin; Wind River formation. 



rium-Eotitanops-CorypJiodon zone (Wind River B); 

 Granger, collector, American Museum expedition, 

 1905. 



Specific characters. — P2-P4, 25 millimeters; nii-ms 

 (referred specimen), 37 millimeters; second and third 

 lower premolars extremely simple, with rudimentary 

 paraconid; ps, metaconid rudimentary, placed very 

 low upon slope of protoconid, talonid narrow, de- 

 pressed, with cingular rudiment of entoconid. (See 

 fig. 238.) 



The extremely simple or primitive structure of the 

 second lower premolar clearly distinguishes this 

 stage. 



A referred specimen (Am. Mus. 14908) collected 

 by Granger (American Museum expedition, 1909), 

 is slightly more advanced in the structure of the second 

 lower premolar (fig. 239) but is still much more 

 primitive than the type of L. popoagicum. 



The measurements of these two specimens are 

 shown below. 



Measurements of Lambdoiherium -priscum, in millimeters 



This Wind River species is identified in Huerfano 

 A by a fine pair of jaws from Garcia Canyon (Am. 

 Mus. 17526). The specific character of pa, without 

 trace of metaconid, is clearly shown in Figure 240. 

 This species is represented by another jaw, with teeth 

 of the same size (Am. Mus. 17528) in which ps, 

 also without metaconid, is in a slightly more advanced 

 stage of evolution, the talonid being broader. 



This species is also doubtfully represented by the 

 imperfect specimen of upper teeth referred to L. 

 popoagicum by Wortman (Am. Mus. 2688), as well as 

 by a newly found specimen (Am. Mus. 17529) of 

 approximately the same size. In this new specimen, 

 found 3 miles east of Gardner Butte, the isolated 

 upper teeth of two sides, including p'-m^, show the 

 following characters: (1) Molars sUghtly smaller than 

 in the referred specimen of L. progressum, (2) conules 

 and cingulum not so well developed, (3) measurements 

 slightly inferior to those of the type of L. popoagicum. 

 (See p. 283.) 



The types of L. popoagicum and L. priscum are both 

 lower jaws from the Wind River, and as there are 

 two lower jaws from the Huerfano positively referable 

 to L. priscum and none referable to L. popoagicum 

 it seems best to assign these two sets of upper teeth to 

 L. priscum also. 



Lambdotherium progressum Osborn 



Text figures 147, 234, 235, 241, 242 

 [For original description and type references see p. 194] 



Type locality and geologic Tiorizon. — Wind River 

 Basin, Alkali Creek, Buck Spring; Lamhdotherium- 



Trh2_ 



P2 



Figure 239. — Incomplete lower jaw of Lambdoiherium priscum 



Natural size. Am. Mus. 14908; Dry Muddy Creek, 18 miles above mouth. A 

 referred specimen. Oblique view of dentition. 



Eotitanops-Coryphodon zone (Wind River B); Granger, 

 collector, American Museum expedition, 1909. 



Specific characters. — P2-P4, 16.5 millimeters. Sec- 

 ond, third, and fourth lower premolars progressive: 

 rudiment of metaconid on P2; Ps with elevated meta- 

 conid subequal with protoconid, broad talonid with 

 rudimentary entoconid; p4 with bifid metaconid and 

 distinct entoconid. 



This is readily distinguished from both L. priscum 

 and L. popoagicum by the advanced condition of ps, 

 which may be described as submolariform. 



