352 MR. A. SMITH WOODWARD ON NEW FISHES [Apr. 15, 



and mandible together are more than twice as deep as broad, and, as 

 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 \ 



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 

 fins 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 com.prises 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 somewiiat more than three-quarters as 

 long as the dorsal, arising behind 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 pro- 

 ceeding 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 tlie specific identity of this fossil with the 

 fine specimen now described, its principal lower teeth being broader in pro- 

 portion to thoir k'ngth and tlic oulcr tcclli relatively smaller. 



