PETERSON : NEW SULLINE REMAINS FROM THE MIOCENE OF NEBRASKA 319 
illustration '° by the latter author, it would seem that, aside from the erroneous defi- 
nition of dental characters by Cope, this species is strongly characterized by its 
short skull and its inflated facial region, and may, when additional material is 
known, justify its retention in the separate genus Chenohyus proposed for it by the 
latter author. 
Thinohyus siouxensis is easily distinguished from other known species by the 
single-rooted p', which has a short diastema in front and a somewhat longer dia- 
stema behind; the unbroken sequence of p? with teeth back of it; the extreme 
posterior position of the posterior narial orifice; the large and anteriorly projecting 
tympanic bulle ; the posterior position of the infraorbital foramen, 7. e., above back 
part of p*, and the absence of p,. The skull of 7. siowxensis is of approximately the 
same size as that of 7. rostratus Cope, but the latter species differs from the former 
in important characters, viz., the two-rooted p', which is separated from the canine 
and p” by diastemata; the latter tooth also has diastemata in front and behind. 
The molar-premolar series is relatively shorter, and the infraorbital foramen is 
placed more in advance (above the middle of p*). In Thinohyus pristinus Cope p, 
is small and as in T. rostratus, two-rooted, ‘the anterior root nearly reaching the 
posterior edge of the canine alveolus, . . . p* 
11 
is wider than long and has but one 
external cusp.” M? is longer than wide, which is due to the large heel. The 
infraorbital foramen is located above the middle of p?, which is another character 
showing similarity to 7. rostratus. According to Sinclair 7. pristinus is farther 
characterized by diastemata in front and behind p,.  T. trichenus Cope has p* as 
12 
long as wide, “and [the tooth] has a sub-quadrate base. P? is small, one-rooted, 
and separated from p? by a short diastema. Premolars one and two in the mandible 
are each separated by diastemata in front and behind. In Thinohyus subequans 
Cope the infraorbital foramen is nearly as far back as in T. siowxensis, 1. e., above the 
middle of p* in the former, and above the posterior part of that tooth in the latter 
species. . swbequans is further characterized by the small two-rooted p’, which is 
17 13 
“almost entirely within the superior canine. P* is wider than long, as in T. 
pristinus and T. siowxensis. In T. subequans there are short diastemata anterior and 
posterior to p;." In Thinohyus lentus Marsh” “p, is separated from the canine and 
10 L. c., Plate XVI. 
"Cope, Proc. Amer. Philos. Suc., Vol. XXXY., p. 73, 1888. 
2D. ¢., p. 7. 
3 Cope, 1. c., p. 69. (The tooth is located close to the postero-internal angle of the canine—O. A. P.) 
™ The lower jaw No. 913 in the Carnegie Museum Collection which is provisionally referred to this species is clearly 
that of a short-faced type such as 7’. decedens. 
‘5 T. socialis Marsh is imperfectly known. It isa John Day form of rather small size with mammillated posterior 
cingulum on m*(?). (See illustration, Am. Jour. Sci., Vol. XLVIII., p. 271, Fig. 25, 1894). 
