1877.] loJ [Cope. 



are no distinct fissures of the surface although these may be represented by 

 some fine parallel lines. 



Vertebras 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 Euglypta, its exclusion from the latter is 

 evident in view of the absence of angular process of the mandible, and 

 the nondiscoidal vertebrae. Its posteriorly placed orbits distinguish it from 

 the genera of his second family, the Braclvyopina, excepting perhaps Bhi- 

 nosaurus. It is with the genera of the third family, the Chaulioclonta, that 

 affinity appears to exist. It is unnecessary to compare Hryops with Lox- 

 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 BMnosaurus the maxillary and mandib- 

 ular teeth are said to be sub-equal. Leptophr actus 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 



