76 Proceedings of the Boyal Fhysical Society. 



Eeturning to the former head (Fig. 3), we find that though 

 the operculars are gone, and most of the other superficial 

 bones fractured and badly seen, the maxilla and mandible 

 occupy their positions. The Maxilla (mx.), the anterior 

 portion of which is deficient in this specimen, at once at- 

 tracts attention by its narrow shape. It is shown in its 

 entirety in the specimen represented in Fig. 4, when it is 

 seen to differ from that of M. Hihherti in the much smaller 

 depth of its posterior expanded portion, that being contained 

 4| times in its length, whereas in that species it is only con- 

 tained about 3 times. The same fact being observable in 

 two separate specimens, it cannot be looked upon as a mere 

 accidental variety in shape. 



The mancliUe (Fig. 5) seldom exhibits the oblique groove, in- 

 dicating the original separation of the dentary element, which is 

 so often observed in M. Rihberti. Jugular plates were present : 

 Ijrincipal (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 proportion than in M. Hihherti, though of 

 the same general appearance. 



The scales and superficial bones of the head have their 

 free surfaces covered with a layer of smooth and brilliant 

 ganoine, which under a lens shows a minute punctation quite 

 similar to that in M. Hihherti. 



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

 portion of the cranial shield are to my mind sufficient evi- 

 dence that the Megalichthys of Burdiehouse is specifically 

 different from M. Hihherti, but I 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. coccolejns or 31. rugosus 

 of Young and Thomson,^ I propose the name of Megal- 



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

 other species of Megalichthys, M. maxillaris (Ag. ) was never described or 

 ligured ; M. prisms (Ag. ), from Orkney, was afterwards referred by Agassiz 

 to Polyphractus (i.e., Dipterus) ; while M. Fischeri (Eichwald) is i)ronoimced 

 by Pander to be portion of the cranial shield of an Osteolepis. 



