306 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



apparent absence of this tritocone may be due to age; 

 it probably has been almost completely worn off. 



The superior incisors arch gently forward, the total 

 transverse series when in place measuring 56 milli- 

 meters; there is a regular increase from i^ to i^; the 

 anterior faces of the crowns are slightly crenulate, 

 and a convex swelling or low ridge surrounds the base; 

 the posterior faces are marked off by lateral ridges 

 and by a posterior cingulum, which is irregularly 

 pitted above; the transverse measurements of the 

 anterior portions of the crown are: i' 10 millimeters, 

 i^ 11 (ap. 12), i' 12. A narrow diastema (7 mm.), 

 separates i^ from the canine. 



The canine has a stout fang and a crown laterally 

 compressed at the base, the measurements being, 

 anteroposterior, 21 millimeters; transverse, 18; height, 

 36 (estimated). The crown is defined by faint 

 anterior and posterior ridges; it is slightly retro verted 

 and inverted. 



In the premolar-molar series a very narrow diastema 

 (5 mm.) separates the canine from p', a tooth which 

 is continuous with the remaining grinders, the total 

 length of the whole grinding series being exactly 141 

 millimeters, less than in the type of L. prisons (149 

 mm.). In MesatirMnus megarhinus the premolar-molar 

 series ranges from 140 to 147 millimeters. P' is a simple, 

 bifanged cone (ap. 11 mm., tr. 8), with faint anterior 

 and posterior concavities on the inner side. P^ is 

 an obliquely placed oval, measuring (ap. by tr.) 12 

 (ectoloph 15) by 15 millimeters, whereas in Mesati- 

 rMnus megarhinus the anteroposterior diameter greatly 

 exceeds the transverse. As Cope pointed out, this 

 tooth is distinguished specifically by the simple 

 rounded protocone, with a more sessile and internally 

 placed tritocone, and a relatively small deuterocone 

 on its lingual side. P^, measuring 15 (ectoloph 18) 

 by 19 millimeters, is broader than long and exhibits 

 relatively more prominent tritocones and deutero- 

 cones. P*, 15 (ectoloph 18) by 21 millimeters, is 

 also broader than long, the tritocones and deutero- 

 cones are still larger, and the external cingulum begins 

 to be defined, as well as the rudimentary anterior 

 and posterior cingula; very rudimentary cingula are 

 also observed in p^, p^, except on the lingual side of 

 the deuterocones, which cusps are absolutely smooth 

 and rounded in all these teeth, presenting in this 

 respect a sharp contrast to the condition in M. mega- 

 rhinus, or even (in less degree) to that in the type of L. 

 priscus. The entire length of the premolar series 

 is 58 millimeters, as compared with 64 in a small 

 individual of M. megarhinus. The molar series 

 measures 84 millimeters. The imperfectly preserved 

 m' (ap. 2.3 mm., tr. 27) exhibits rudimentary external 

 and antero-internal cingula and a subquadrate crown; 

 in m^, also badly damaged, we observe evidence of 

 sessile conules and a low anterior cingulum; in the 

 better preserved m' (ap. 30 mm., tr. 35), also a sub- 

 quadrate tooth, there are rudimentary external. 



anterior, and postero-internal cingula, the last giving 

 rise to a low cingulate hypocone; there is some evi- 

 dence of small, well-worn protoconules and metaco- 

 nules; the crown, as in the other molars, is singularly 

 smooth. 



SlcuU. — Although only the anterior portion of this 

 cranium is present (see fig. 258), it affords conclusive 

 evidence of ancestral relationship to L. laticeps in 

 the rounded shape of the nasals. Its general or 

 palaeosyopine characters are especially seen in (1) the 

 downward V-shaped extension of the nasals on the 

 sides of the face; (2) the prominent antorbital Icnob of 

 the lacrimals; (3) the backward extension of the 

 infraorbital portion of the maxillaries beneath the 

 malar arch; (4) the narrow median symphysis between 

 the premaxiUaries; (5) the comparatively slight lateral 

 decurvature of the nasals; (6) the extreme upward 

 arching of the zygoma as a whole, the mid-depth 

 being 51 millimeters, and the "depression and angula- 

 tion" of the malar 19 millimeters behind the orbits. 



This cranium not only differs in its smaller size but 

 in a number of other proportional characters from that 

 of L. laticeps. The nasals are relatively more elongate, 

 narrower posteriorly, and relatively broader an- 

 teriorly — that is, the sides of the nasal in front of the 

 narial notch are more nearly parallel, the narrowest 

 midportion measuring 44 millimeters, the broadest 

 terminal portion measuring also 44. From the an- 

 terior border of the orbit to the narial notch the 

 measurement is 61 millimeters. The zygomatic bar 

 immediately below the orbit is more angulate and less 

 rounded than in P. leidyi, the inferior face of the 

 malars being more flattened and the sharp masseteric 

 ridge defining the malars inferiorly being less extended 

 fore and aft. In palatal view we observe the trans- 

 verse extension of the glenoid facets for the condyles 

 of the jaw, the opening of the nares behind m^, the 

 abbreviation of the palatines, and the relative flatness 

 of the palate. 



Limnohyops prlscus Osborn 



Plates LVI, LX, LXII; text figures 29, 115, 219, 254, 256, 



259, 260, 266, 274, 690, 717, 745 



[For original description and type references see p. 180] 



Type locality and geologic horizon. — Grizzly Buttes, 

 west Bridger Basin, Wyo. ; Bridger formation, Palaeo- 

 syops paludosus-Orohippus zone, level Bridger B 2. 



Specific characters. — P^-m^ 148 (type) to ?161 milli- 

 meters. Second superior premolar obliquely elongate 

 with a very rudimentary tritocone. Large hypocone 

 on m^. 



This is apparently a larger and relatively more 

 advanced animal than L. laevidens, but, as the specific 

 designation priscus indicates, it is still very primitive. 



Materials. — L. priscus is represented by the type 

 skull (Am. Mus. 11687; see fig. 259), from the 

 Bridger formation at Grizzly Buttes, level B 2, and 

 by the type or cotype jaw (Am. Mus. 11688), found 



