Prof. Morris — On the Genus uEchmodus. 339 



to the commencement of the caudal fin exactly equal to the breadth 

 of the flank from the ventral to the commencement of the dorsal 

 fin. Scales twice as broad as long, and rectangular as far as the 

 middle of the large opercular plate, gradually becoming smaller to- 

 wards and near the dorsal line ; scales smooth and more or less 

 crenated posteriorly. (The line of lateral scales perforated by the 

 mucous canal, although not distinctly marked in the specimen 

 figured in the plate, is more clearly seen in some of the specimens 

 in the British Museum.) The nuchal scales are marked by elongated 

 tubercles which decrease in size and number, and finally disappear 

 before reaching the dorsal fin. The pedicle scales are longer than 

 broad and rhomboidal ; dorsal fin nearly half the length of the body, 

 commencing nearly opposite the ventral fins, and ending near the 

 pedicle of the tail, the rays, about thirty in number, diminishing in 

 size posteriorly ; pectoral fins very small (about twelve rays), ventral 

 (six or seven rays) small, placed midway between the pectoral and 

 commencement of the anal fin, which is nearly one-third the length 

 of body, and has about twenty rays, and is continued nearly to the 

 caudal fin. Caudal fin moderately large, squarish, rays about 

 twenty-four in number, which bifurcate at a short distance from 

 their origin, and are further subdivided, the upper and lower rays 

 with fulcra, in a single series. 



General form of head sub-oval ; the orbital, opercular and sub- 

 opercular, and other plates are coarsely tuberculated.. The tubercles 

 being somewhat adpressed and more or less elongated. The branchi- 

 ostegous rays five ? on each side. 



The length from the snout to the extremity of tail is about 8 inches, 

 the height 4| inches ; length of body from opercular plate to the 

 commencement of tail 5 inches ; length of head from the snout to 

 posterior part of opercular bone If inches ; depth of head 2^ inches. 



The bones of the head are somewhat displaced and broken, the 

 maxillary crushed and distorted, but the opercular, sub-operculax, 

 and dentary bones, as also the branchiostegous rays are well shewn. 



There are in the National Collection no fewer than six specimens 

 of this Liassic fish agreeing closely both in size and proportions, 

 and quite as well preserved as the specimen figured in our 

 Plate. 



It is interesting, too, to notice that whereas the other species of 

 JEchmodus and Dapedius are exceedinglj'- variable in proportions — 

 indicating several distinct species — the fish before us is well-marked 

 and quite specifically distinct from any figured by Agassiz, or de- 

 scribed by Sir P. Egerton. 



The figure in the Poissons Fossiles, which most closely approaches 

 it, is the ^chmodus pliolidotus of Agassiz, from the well-known Lias 

 locality of Boll, in Wurtemburg (see Poiss. Foss., pi. 23e, fig. ii.) ; 

 but from this species it is distinguished by its more orbicular outline 

 (resembling that of Dapedius orbis, Ag. Poiss. Foss. Tab. 25d) and 

 by the length of the pedicle, the form of the tail and character of 

 the scales, which are longer than in the specimen figured by Agassiz. 



The uEchmodi are rather short sub-orbicular, compressed-bodied 



