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Show 352 MR. A. SMITH W O O D W A R D O N N E W FISHES [Apr. 15, and mandible together are more than twice as deep as broad, and, usual in the genus, the facial profile below the frontal angulation is vertical. The operculum (op.) is small, having a coarse, radiating, fibrous appearance, possibly not merely superficial, but textural; it is irregularly triangular in shape, its depth being at least twice as great as its maximum breadth, and the postero-inferior angle apparently well-rounded. Dentition.-The jaws and teeth are so much crushed as not to be readily determinable ; but the principal teeth are not more than twice as broad as long, while the others are of considerable relative size and round. Appearances are also suggestive of there being only two outer series of teeth in the mandible l. Vertebral Axis.-There is the ordinary vacant space denoting a persistent notochord, and the small expansions of the bases of the neural and haemal arches are partly seen. There are not less than 13 segments in the abdominal region, and 20 in the caudal, these exhibiting the usual form and proportions. Appendicular Skeleton.--To the remains of the pectoral arch behind is fixed a large expanded fin, situated well upon the side of the fish. It consists of numerous broad delicate rays, doubtless closely articulated, and very divergent distally. The ventral margin that would support the pelvic fins is broken away: but the median tins are well preserved, except the distal portion of the anal. Their rays, like those of the pectoral, are broad, closely articulated from a point near the base, somewhat spaced, and branching distally. The dorsal fin arises at the middle point of the trunk, and comprises 39 rays, of which the fifth or sixth is probably the longest, its length being nearly half that of the base-line of the fin. The anal fin comprises about 30 rays, is somewhat more than three-quarters as long as the dorsal, arising bebind the latter, but terminating at the same point quite at the end of the caudal pedicle. The caudal fin has a narrow base, and its rays are most slender and clustered at the dorsal and ventral borders; the median rays are sparser and more robust, but scarcely extend further back than the lateral rays, thus imparting to the fin a truncated, rather than a rounded form. Scales.-The thickened ribs of about fifteen vertical series of scales are observed in the abdominal region, the hindermost proceeding from a point slightly in advance of the dorsal fin and meeting the origin of the anal. There are also traces of the serrated dorsal and ventral ridge-scales, but these seem to have been small. Generic and Specific Determination.-The form and proportions of the head, caudal pedicle, and caudal fin demonstrate that the fish now described is truly referable to Mesodon ; and it is one of the most complete examples of the genus hitherto made known. The circumstance that so few details are forthcoming as to the 1 In the imperfect specimen mentioned above (p. 351) there are distinctly only two series of teeth external to the principal row in the mandible ; but the present writer is inclined to doubt the specific identity of this fossil with the fine specimen now described, its principal lower teeth being broader in proportion to their length and the outer teeth relatively smaller. |