76 



Mr. R. Walker on Fossil Fishes of Dura Den. 



in the Museum of Practical Geology," &c. He further states, 

 ''The clear recognition of the fact that this elegant structure 

 really characterizes Glyptolepis is of great importance, for it en- 

 ables one to discriminate between Holoptychius (whose scales 

 have no semilunar area of backwardly-directed points) and Gly- 

 ptolepis." As we have just seen, the scales of H. Flemingii, Agass., 

 have the identical structure of the scales of undoubted specimens 

 of Glyptolepis, so far, at least, as the crescent of points is con- 

 cerned, which seems to be the only tangible difference between 

 them generically [Holoptychius and Glyptolepis). Such being 

 the case, we are warranted in pronouncing H. Flemingii to be a 

 true Glyptolepis. 



The head of H. [G.) Flemingii is in length to that of the body 

 as 1 to 4 or 5, and is of a depressed roundish form, gradually 

 tapering towards the snout, which is blunt and round. The 

 head is covered with granulated plates of no great thickness ; 

 on the sides of the head they join each other by squamous su- 

 tures, extending inward and upward. In this way these bones 

 slightly overlap at the margins, without projecting externally. 

 When their granulated surfaces happen to be uninjured, it is 

 not always easy to determine where one bone ends and another 

 begins. The occipital region is covered over by a median and 

 two lateral bones; the median, or supra-occipital (s.o.), is trun- 

 cated in front and rounded behind, where it partly overlaps the 



Fig. 3. 



Side view of the head of H. Flemingii. 



scales of the nape. The lateral or epiotic (ep.) extend back- 

 wards and downwards till they meet the operculum, their upper 



