1877.] 189 
(Cope. 
are no distinct fissures of the surface although these may be represented by 
some fine parallel lines. 
Vertebre referred to this genus are small in proportion to the dimen- 
sions of the skull. They are not discoidal but somewhat elongate ; are 
biconcave, and are not perforated for the notochord. The middle portion 
of the centrum is contracted. One articular extremity has the borders of 
the concave centre, convex. Zygapophyses large. Ribs present short ; 
neural spines elongate, stout. 
In comparing this genus with those described by authors and arranged 
by Mr. Miall in his family Huglypta, its exclusion from the latter is 
evident in view of the absence of angular process of the mandible, and 
the nondiscoidal vertebrx. Its posteriorly placed orbits distinguish it from 
the genera of his second family, the Brachyopina, excepting perhaps Rhi- 
nosaurus. It is with the genera of the third family, the Chauliodonta, that 
affinity appears to exist. It is unnecessary to compare Hryops with Loa- 
omma, which has immense and irregularly shaped orbital openings, and 
trenchant teeth ; but with Zygosaurus and Melosaurus the affinity is closer. 
The deep postorbital depressions, and the grooved maxillary teeth, de- 
scribed by Eichwald in the former genus, separate it at once. The teeth 
of Melosaurus are equally distinct, being, according to Meyer, conical and 
deeply grooved at the base. In Rhinosaurus the maxillary and mandib- 
ular teeth are said to be sub-equal. Leptophractus has deeply grooved 
teeth with strong cutting edges. 
Char. specif.—In this category I include many of those introduced into 
the generic diagnosis by Mr. Miall in the very useful report to the British 
Assoc. for the Advancement of Science, 1874, p. 149, by the Committee 
on the Structure and Classification of the Labyrinthodonts. Such are the 
width of the interorbital space, the outline of the muzzle, the details of 
the sculpture, the approximate number of the teeth, etc. 
The cranium has a sub-triangular outline, with the sides a little longer 
than the base, and the apex (muzzle) very obtuse. The profile is elevated 
behind, and the sides slope steeply to the mandible ; the slope of the muz- 
zle is rather steep, but less so than that of the cheeks. The extremity of 
the snout is broadly rounded and depressed, and overhangs the mandible. 
The supra-occipital outline is concave, and the epiotic angles only mode- 
rately prominent. The quadrate bones extend far posteriorly, and are 
horizontal above at their distal extremities. The orbits are nearly round, 
although somewhat wider than long, and they are directed equally out- 
wards and upwards. The inner margin is slightly flared upwards, and it 
terminates anteriorly and posteriorly in a slight tuberosity, at the junction 
with the canthus rostralis and temporal ridge respectively. 
The orbit occupies the anterior portion of the posterior third of the length 
of the skull, including the epiotic angles; and its long diameter is one- 
seventh that of the skull from the epiotics to the muzzle inclusive. The 
same diameter is about half of the interorbital width. The parietal re- 
gion is plane, the frontal gently concave, and the muzzle depressed convex 
