162 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



Type locality and geologic horizon. — Near Henrys 

 Fork, Wyo.; Uintatherium- Manteoceras- Mesatirhinus 

 zone (Bridger C or D). F. Mead, jr., collector. 



Holotype. — A fragmentary skull including nasals and 

 palate with teeth (Yale Mus. 11122). 



Characters. — Marsh writes: 



The present species may be distinguished from those above 

 described [Palaeosyops laticeps Marsh, Tdmatherium validum 

 Marsh], especially by the strong basal ridge of the molars. On 

 the last lower molar it extends entirely around the posterior 

 lobe. The first of the upper true molars has the two inner 

 cones nearly of the same size. The small intermediate median 



FiGTJRE 95. — Cope's cotypes of Palaeosyop. 



After Cope, 1884. Ai, Lett mandibular ramus, superior view Oeetotype, Am. Mus. 5098); Aj, internal view otsame; 

 B, left upper premolars and molars (Am. Mus. 5097); Ci, third left superior molar, crown view; Ct, the same, buccal 

 view (Am. Mus. 5099); Di, fourth superior premolar, crown view; Dj, the same, buccal view (Am. Mus.). 



tubercles are well developed on the upper molars, and all the 

 teeth are strongly rugose, even in fully adult animals. The 

 nasal bones contract anteriorly and are rounded in front. 

 The outer margin is decurved and thickened. The premaxil- 

 laries unite by a very short median suture, similar to that in 

 Palaeosyops laticeps. The zygomatic process of the squamosal 

 is stout but much compressed, thus differing widely from both 

 the species already described. 



Measurements [Marsh] 



Millimeters 



Anteroposterior extent of last three upper molars 110 



Anteroposterior diameter of last upper molar 41 



Transverse diameter 43. 5 



Anteroposterior diameter of last lower molar 51 



Etymology. — robustus, robust; in allusion to the stout 

 skull and dentition. 



Present determination. — The species is probably a 

 valid one, referable to the genus Palaeosyops. 



Limnohyus Leidy (not Marsh), 1872 

 Cf. Palaeosyops, this monograph, page 155 

 Original reference. — Acad. Nat. Sci. Philadelphia 



Proc, 1872, pp. 240-242; published December 17, 



1872 (Leidy, 1872.1). 

 ^ As we have seen above, Marsh's genus Limnohyus is 



simply a synonym of Palaeosyops, which had been 

 defined by Leidy as having 

 "but a single lobe to the inner 

 part of the crown " of the "last 

 upper molar." In 1872 Leidy, 

 after pointing out this fact, 

 says that the name Limnohyus 

 "might with propriety be 

 applied to the animal with 

 molars like those of Palaeo- 

 syops except that the last upper 

 one has two inner cones to the 

 crown." This doubtless sug- 

 gested Marsh's subsequent 

 term Limnohyops. Lim- 

 nohyus Leidy is thus preoccu- 

 pied by Limnohyus Marsh, 

 which is a sj'^nonym of 

 Palaeosyops. 



Etymology. — Xifivrj, a marshy 

 lake; Cs, boar. 

 Palaeosyops vallidens Cope, 1872 



Cf. DoKchorhinus vallidens (Cope), 

 this monograph, page 401 



Original rejerence. — -Pal. 

 Bull. No. 7, dated "Aug. 22, 

 1872"; Am. Philos. Soc. Proc, 

 vol. 12, p. 487, 1873 (Cope, 

 1872.1). 



Subsequent reference. — Ter- 

 tiary Vertebrata, p. 699, pis. 

 51, fig. 1; 52, fig. 3; 53, fig. 1; 

 36, figs. 10, 10a, 11, 11a, 1884 

 [1885] (Cope, 1885.1). 



Type locality and geologic 

 horizon. — -"Mammoth Buttes, southwestern Wyoming, 

 near the headwaters of Bitter Creek," Washakie Basin; 

 Eobasileus-Dolichorhinus zone (Washakie B 2). 

 Characters. — Cope writes: 



Represented by the dentition of one maxillary bone with 

 other bones of one individual [Cope, Am. Mus. 5097]; a portion of 

 the same dentition of a second [No. 5099]; with both rami of 

 the mandible with complete dentition of a third [No. 5098]. 

 The species is distinguished by the details of the dental struc- 

 ture and by the superior size. It exceeds, in this respect, the 

 Palaeosyops major Leidy; while the three posterior lower molars 

 measure 4.5 inches in length, the same teeth of the present 

 animal measure 6.25 inches. The last superior molar of an- 

 other specimen measures 2 inches in length; in the third the 



