2 



BRITISH FOSSILS. 



justifiable in this case for the purpose of perpetuating the name of 

 the talented discoverer of Macropoma Mantelli. The remains of 

 this fish are most numerous in the chalk formations of the south 

 of England, and are all referable to one and the same species. The 

 subject of this article constitutes a second species of the genus found 

 in the Gault at Speeton, in Yorkshire. The specimen which is in 

 my possession is unique, and Professor Agassiz did me the honour 

 of naming it after me. 



Description. — The reasous assigned by Professor Agassiz for 

 considering this a distinct species in the short allusion he makes to 

 it in the " Poissons Fossiles/' are, ''the more uniform character of the 

 scales, and differences in the form of the head.'' These and other 

 specific peculiarities will be treated of in the sequel. The specimen 

 exhibits only the anterior half of the fish ; comprising the head, 

 the pectoral fin, and the first few rays of the dorsal fin. It evidences 

 a fish of the largest dimensions attained by the Mantellian species. 

 The head from the snout to the posterior edge of the operculum 

 measures seven inches; the depth at the occiput is five inches and a 

 half, and the breadth across the frontal bones three inches. The 

 inclination of the profile line of the head is very steep from the 

 occiput to the orbit, far more so than in the allied species ; the orbit 

 is situated in a more advanced position, and the facial line thence to 

 the snout falls much more rapidly. The opercular apparatus covers 

 a far larger area, and the breadth of the cranium is comparatively 

 greater. The orbit in this species is large, and a portion of the 

 capsule of the eye is preserved. The frontal bones are wide, coarse 

 in texture, and bear a few scattered granules on their exterior 

 surface. The borders of the upper jaw are formed by the superior 

 maxillary bones, which are very broad ; they are beset with very 

 numerous sharp pointed teeth, closely arranged and of uniform size. 

 The lower jaws are also very broad, and the space between the 

 rami is closed by a single glossohyal plate, as in Lophiostomiis, 

 Arapaima, and ^ mm. The lines of demarcation between the oper- 

 cular bones are not discernible, but the entire apparatus is consider- 

 ably larger than the corresponding parts of Macropoma Mantelli. 

 The pectoral fin is of large dimensions. This organ is not mentioned 

 in the description of Macropoma Mantelli, nor is it well seen in 

 any of the specimens of that species 1 have examined. It may or 

 may not, therefore, be a distinctive and specific character. The fin 

 is by no means perfect in my specimen, but it measures four inches 

 and a half in length, by two inches in breadth. The rays are very 

 numerous, and differ from those of the dorsal fin by being dichotom- 



