500 the osteology of hy^nodon. 
tritocone on and P^, the slenderness of the canines and the shallowness of the face^ 
T of tl.e racial portion of the skull and many fragments of 
the ekrieto'u, including a nearly complete hind-foM. It was found by Mr. Hatoher 
in the lower l>,-otoceras-beds (upper part of the While River horison). 
In the following descriptions, account will be taken of the peculiarities of each 
species so far as these are known. The specific differences refer principally to 
variations of size ; in important structures there is great constancy. 
T rvxjT? riT^XTTTTTOISr 
The structure of the teeth has long been accurately known and needs no de- 
tailed account. The incisors and canines are entirely of the carnivorous type, the 
external upper incisor much enlarged, and the second lower crowded back out of 
line with the other two. The upper premolars are very simple, essentially com- 
pressed cones, with more or fewer additional cusps. In N. crzientus p2 has no pos- 
terior cusp, which is present in the other species. In the former, and in H. horri- 
dus, this tooth has an exceptionally high crown. On the tritocone is always 
present. The fourth premolar has all the elements of the carnivorous sectorial ; 
but the deuterocone, though supported on a large fang, is itself but little developed, 
and the tritocone is too small to form an efficient shearing blade. In the smaller 
species, H. crucians, H. pmicidens^wyH H. mzislelinus, is a small antero-cxternal 
basal cusp. H. pancidezzs is altogether excejotional in lacking Pi and in having 
placed very obliiinely to the line of the jaw. The upper molars arc highly cliarac- 
tcristic. The protocone is lost, though its fang is retained. The para- and meta- 
cones are very closely approximated, and on “2 are in distinguish ably fused together ; 
a long and trenchant posterior ridge forms a very efficient shearing blade, especially 
on which is much the larger of the two. 
The lower premolars are likewise of very simple construction. The first has 
always a very low crown, but is much elongated from before backward. In H. erzt- 
entzis p 2 and pS have no talon (rnetaconid), which is present on p 4 ; in H. pazicidens 
the talon is present on p3 as well as fi4, and in H. cruciazis and H. horridiis it is 
present on all the premolars except the first. In H. pazicidezis pi is smaller than 
in the other species, and p3 has the same oblique position as in the upper jaw. The 
first molar is one of the smallest teeth in the lower series; its crown consists of 
three cusps m the same antero-posterior line, a high protoconid and lower para- and 
hypocomd, the rnetaconid having disappeared. The second molar is composed of 
compressed proto- and paraconids form an 
httri„rth T ■“»« offirient and more simplified, 
ditio. ” - "'lylh however, is sometimes retained in a rudimentary con- 
sC" r-T f “PP- “■'<1 lowoh fs the 
of all the cheek teeth.'™* ~ "“o> 11“ trenchant form 
