212 
THE GEOLOGIST. 
Ptychognatlms declivis, Ow. — Plane of occiput meeting the upper (fronto- 
parietal) plane at an acute angle, rising from below upward and backward, as in 
the feline mammals ; fronto-i)arietal i)lane bounded by an anterior ridge, ex- 
tending fi-om one superorbital process to the other ; from this ridge the facial part 
of the skull slopes downward in a straight line, slightly diverging from the parallel 
of the occipital plane ; superoccipital ridge much produced and notched m the 
middle ; the occipital plane, owing to the outward expansion of the mastoid 
plates, is the broadest part of the slcull, which quickly contracts forward to the 
ridged beginnings of the alveoli of the canine tusks ; orbits oblong, reniform, 
suggestive of tiie rei>tile having the power of turning the eyeball, so as to look 
upward and backward as well as outward. Remains of sclerotic plates. Nostrils 
divided by a broad, flat, upward production of j)remaxillary, situated nearer the 
orbit than the nuizzle, smaller than in ty^ie Dicynodon ; temporal fossae broader 
than long, and with the outer border longest ; palate with single large oval vacuity, 
bounded by palato-pterygoid ridges ; occipital nypapopliyses proportionally thicker 
than in Dicynodon tigriceps ; no trace of median sutiu-e in parietal, which is per- 
forated by a foramen i)arietale ; frontals divided by a median suture ; supi)ort a 
transverse pair of small tuberosities ; anterior boundaiy-ridge of vertex formed by 
the nasals and prefi-ontals, the outer surface of both being divided into a horizontal 
and sloping facet ; lacrymal bone extending from fore-part of orbit half an inch 
upon the face to nostril ; premaxillary long and single, its median facial tract 
liat, with a low median longitudinal ridge ; maxillaries forming the lower boundary 
of the nostrils, and uniting above with the prefrontal lacrymal and nasal bones, their 
outer surface divided by the strong ridge suggesting the subgeneric name ; teeth 
of the upper jaw restricted to the two canine tusks, the sockets of wiiich descend 
much below the edentulous alveolar border ; lower jaw edentulous, deep, and 
broad, with the fore-part of the symphysis produced and bent up to meet the 
seemingly trmicate end of the premaxillary, a character indicating, with the 
angular outhne of the skull, the subgeneric distinction. 
Ptychognathus verticalis. — The skull of this species, repeating the subgeneric 
characteristics of the foregoing, has the facial contour descending almost vertically 
from, and at almost a right angle with, the fironto-parietal plane. Orbits propor- 
tionally larger and more fidly oval. Ridged sockets of the canine tusks descending 
more vertically fi-om below the orbits. Originals transmitted by Governor Sir 
Geo. Gray, K.C.B., from Rhenosterberg, South Africa. 
Subgenus Oudenodon, Baiu {ovSeis, none, oSovs, tooth). The skull in this sub- 
genus presents the divided nostrils, the structure and the rounded contours of 
that of the true Dicynodons ; also the same form, relative size and position of the 
orbits and nostrils ; but the zjrgomatic arches are more slender, straight and long ; 
and, although there be an indication of an alveolar process of the superior maxillary, 
the lower part of which projects slightly beyond the rest of the edentulous border 
of the jaw, it does not contain any trace of a tooth, so that both jaws are edentu- 
lous, a character which had attracted the attention of their discoverer, Mr. Bain, 
who, in indicating it, proposed the name Oudenodon. 
It is permissible to speculate on the possibility of these toothless Dicynodontoids 
being, after the analogy of the Narwhals, the females ; or of their being in- 
dividuals which had lost their tusks without power of replacing them, as 
the known structure of the true Dic3aiodons indicates. But there are 
characters of the zygomatic arches and temporal fossae which differentiate the 
toothless skull sufhciently to justify their provisional reference to a distinct 
subgenus. 
Hyoid apparatus of Oudenodon. — Beneath one of the skulls, and imbedded in 
the matrix between the mandibular rami, were the following elements of the 
hyoid apparatus : — basi-hyal, cerato-hyals, thyro-hyals (or hypo-brancluals), cerato- 
branchials, and uro-hyal. 
The cerato-hyals are long, subcompressed, exiianded at both ends ; the thyro- 
hyals shorter and more slender ; the cerato-branchials with a sigmoid flexiu'e ; the 
uro-hyal symmetrical, broad, flat, semicircular, with a production like a stem from 
the middle of the straight anterior margin. This apparatus shows the complexity 
by which that in Lizards and Cheloiuans differs from the hyoid in Crocodiles, and 
