2 



BRITISH FOSSILS. 



tions. The remnant of one of the opercular bones shows that this 

 pattern did not extend to those bones ; they seem, however, to 

 have been covered with a fine and rather indistinct granulation, 

 intermixed with raised lines, running parallel to the posterior margin 

 of the flap. The teeth are numerous in both jaws. The larger ones 

 are conical, sharp, and hooked at the extremity. The smaller ones 

 are of the same form, and fill up the irregular interspaces between 

 the larger ones. They together form a single row, fringing the 

 margins of the mouth. The symphisis of the lower jaw is remarkably 

 acute. The branchiostegous rays are beautifully displayed, occu- 

 pying the angle between the jaws. There appear to have been 

 about twelve on either side. The pectoral fins are composed of a 

 series of flattened rays, about thirty in number. They are devoid 

 of transverse articulations, but dichotomise when near their ex- 

 tremities. The ventral fins are situate nearer to the anal than to 

 the pectoral fins. They are smaller than the latter, although larger 

 than the corresponding organs in the allied genera. They contain, 

 in addition to three or four small marginal appendages, about 24 

 rays. These are rounded, have frequent transverse articulations, and 

 bifurcate at their extremities. The anal fin is short and small. It 

 occupies a position midway between the anterior insertion of the 

 ventral fins, and the commencement of the tail. It contains 16 or 

 18 rays of similar character to those composing the ventral fins. 

 The scales are small, and very numerous. They vary in form and 

 size, on difierent parts of the body, but they all correspond in the 

 character and distinctness of the surface ornament. This consists 

 of elevated ridges of enamel, arranged for the most part in longi- 

 tudinal directions, in reference to the outline of the fish, but 

 obliquely as regards the individual scales. On the nape a few 

 granulations are interspersed with the ridges. The latter, however, 

 predominate in all other regions of the body. The scales near the 

 tail are thicker than those on other portions of the trunk, and the 

 ornament more coarse. Each scale has a thick rib on its under 

 surface, which locks in reciprocally with that of the adjoining scale, 

 and secures the continuity of the series against accidental dis- 

 location. 



Affinities. — The character of the scales alluded to above marks 

 out the genus Oxygnathus, as distinct from all others. The only 

 approach to it is in the genus Acrolepis, but (in addition to the 

 latter being aheterocerque fish, which alone would forbid the union,) 

 the differences in the form of the scales, and the arrangement of the 

 sculpture, sufficiently distinguish it from that genus. A slight re- 



