Dr. R. H. Traquair — On the Genus Megalichthys. 121 



The same fact being observable in two separate specimens, it cannot 

 be looked upon as a mere accidental variety in shape. 



The mandible (Fig. 5) seldom exhibits the oblique groove, indi- 

 cating the original separation of the dentary element, which is so 

 often observed in M. Hibberti. Jugular plates were present ; principal 

 (Fig. 6), median and lateral, but these do not call for any special 

 comment ; nor do the opercular bones, which are sometimes found 

 detached, and exhibit the ordinary shape. 



The teeth are seldom seen : when visible, they appear rather smaller 

 in projDortion than in M. Hibberti, though of the same general appear- 

 ance. The scales and superficial bones of the head have their free sur- 

 face covered with a laj^er of smooth and brilliant ganoine, which under 

 a lens shows a minute punctation quite similar to that in M. Hibberti. 

 The difference in shape of the maxilla and of the parietal portion 

 of the cranial shield are to my mind sufficient evidence that the 

 Megalichthys of Burdiehouse is specifically different from M. Hibberti ; 

 but 1 have no doubt that when both species are more minutely 

 examined and described, many other points of distinction will be 

 found. For the form above described, which is certainly still less 

 likely to be confounded with either the M. coccolepts or M. rugosus of 

 Young and Thomson,' I propose the name of Megalichthys laticeps. 

 Possibly its remains may include those of Biplopterus Robertsoni, Ag. ; 

 but as this is a mere MS. name, to the original of which there is now 

 no clue, it must be simply cancelled. 



Its remains are for the most part considerably smaller than those 

 of the common Coal-measure species, though patches of scales occur 

 showing that it sometimes attained a size nearly as great. 



The fact that this species, of Calciferous Sandstone age, is distinct 

 from any yet found in the Coal-measures, is in accordance with the 

 result of all my experience in the domain of British Carboniferous 

 Ichthyology, namely, that very few species of Ganoids are common 

 to the strata above and below the Millstone Grit. As regards 

 Megalichthys, however, it must also be mentioned that its scattered 

 remains are not uncommon in the estuarine beds of the Scottish 

 Carboniferous Limestone Series, but as yet I have seen no specimen 

 on which any secure determination of species can be founded. 

 EXPLANATION OF PLATE V. 

 All the specimens figured are in the Edinburgh Museum of Science and Art. 

 Fig. 1. Megalichthys laticeps, Traq. Entire specimen, reduced : original 10|- 

 inches in length. Hugh Miller Collection. 

 J, 2. Hinder extremity of another specimen, showing the second dorsal, anal, 



and caudal tins : reduced one-half. 

 ,, 3. Head of another specimen showing the cranial buckler, maxilla and 



mandible : reduced more than one-fourth. Hugh Miller Collection. 

 „ 4. Maxilla, from another head : natural size. Hugh Miller Collection. 

 ,, 5. Mandible reduced, placed upright to save space : original 'l\ inches long. 

 ,, 6. Principal jugular plate, reduced : original 2^ inches in length. 



1 Proc. Brit. Assoc. 1869 (Exeter), Trans, of Sections, p. 102. As regards other 

 species of Megalichthys, 31. muxiltans, Ag., was never described or figured; 

 M. pnscus, Ag., from Orkney, was afterwards referred by Agassiz himself to I'oiy- 

 phractus {i.e. JJipterus) ; while M. Fisoheri, Eichwald, is pronounced by Pander 

 to be portion of the cranial shield of an Osteolepis. 



