40 BRITISH FOSSILS. 



Four views (one-half the size of nature) of the head of this fish 

 are given in PL X. ; it is composed of a parieto-occipital and a 

 frontal moiety, as in Macropoma, and the former (Pa) is divided 

 by a median suture into two. The frontal shield is greatly 

 crushed, and its precise form cannot be made out, but so much of 

 it as remains is like that of Macropoma. 



The general arrangement of the suborbital bone or bones (figs. 

 2 and 3) is plainly similar to that in Macropoma ; and the same 

 likeness extends to the operculum (Op), to the strong pulley- 

 like end of the quadrate (Qu), — divided in the present fish by a 

 longitudinal depression, so as to resemble the articular end of 

 a phalanx, — and to the lower jaw. 



I suspect that b, fig. 2, represents the post-maxillary bone of 

 the Chalk Macropoma, in which case the flat bone a (figs 2 and 3) 

 will probably be the suboperculum. 



The jugular bones (fig. 4, G) are double, and closely resemble 

 those of Macropoma in form : they present an ill-defined rugosity, 

 but no proper sculpture, and no trace of enamel, resembling in this 

 respect the opercula and the other bones of the head. 



At a, fig. 4, clear traces of ossified branchial arches are visible. 



In its general characters it is clear that this fish completely 

 resembles Macropoma ; and considering the frequency with which 

 the enamel is found to have disappeared from the cranial bones of 

 fishes of the latter genus in the Chalk, no weight can, I think, 

 be attached to this apparent difference. 



The scales are quite similar to those of Macropoma in form, and 

 in the proportion of the sculptured to the unsculptured part (the 

 unsculptured part in the scale 3 of plate 65 b of the' " Recherches " 

 is far too small), but the enamel tubercles are far less regularly 

 oval, and tend to become elongated and ridge-like. 



I think, therefore, that this may safely be regarded as a dis- 

 tinct species, for which I propose the name of Macropoma 

 substriolatum. 



I am indebted to Prof. Sedgwick and Mr. H. Seely, for the 

 opportunity of figuring and describing the specimen on which 

 this species is based. 



