Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/414

 surface, on the other hand, being rather convex than concave. A portion of the membranous fin is seen attached to the hinder edge of the spine, and is composed of fine-grained shagreen ; impressions are faintly seen in other parts of the specimen, which show that the dermal covering in general was of the same character. The outline of the mandibular region is fortunately preserved, and exhibits a very singular truncated form of lower lip. The labial and mental angles are right angles, and connected by a straight line one inch in length ; the upper and lower margins are nearly parallel for a distance of one inch from the mentum ; so that the area of the anterior mandibular projection was a square of one inch. The dental apparatus is rather dislocated ; but the component parts remaining are well preserved. There is an indistinct impression of the left maxillary plate in its proper position ; but its fellow of the right side (1 e) is thrown back below the orbit. This measures one inch and a quarter in length by three lines in width, being of slighter proportions than the corresponding denticle of Ischyodus Egertoni, which it most resembles. The premaxillaries are absent. The mandibular plates (1f) are reversed, but retain their relative positions. Each measures one inch and a half in length, and is one inch deep at the symphysis. The dental apparatus corresponds in all respects with the characters assigned by me to Ischyodus, to which genus I refer this specimen ; but as it differs specifically from those already described, I have selected a name signifying its peculiar deviation from the recent types in the size and form of the rostral appendage.

This remarkable specimen has been secured for the fine collection of fossil ichthyology in the British Museum.

DESCRIPTION OF PLATE XIII.

Fig. 1. Ischyodus orthorhinus, reduced one-third : a, labial prolongation ; b, frontal appendages ; c, dorsal spine ; d, articulation of the dorsal spine ; e, maxillary plate ; f, mandibular plates.

Fig. 2. Rostral tubercle, magnified.

Fig. 3. Outline of the anterior parts of Callorhynchus antarcticus, reduced one-half: a, labial prolongation; b, frontal appendage; c, dorsal spine; d, articulation of dorsal spine.

Discussion.

Dr. Gunther commented on the interest of this discovery, as in no other Sharks is the same articulation of the dorsal spine as that described in the paper to be found. He inquired whether the granulated plate supposed to be dorsal might not be a part of the armature of the lateral line, as in Sturgeons. He thought that the Chimaeroids would eventually prove to be intermediate between the Ganoid and Shark types, and that all belonged to one subclass.

Mr. Gwyn Jeffreys inquired what other remains were found with these fishes such as might represent the food, molluscan or otherwise, on which they lived.