70 Proceedings of the Roycd Physical Society. 



" family " importance, its structure conforms closely to that 

 of Osteolepis. 



The resemblance of the scales in external form is 

 sufficiently obvious to every one, and their close correspond- 

 ence in microscopic structure may be seen by comparing the 

 figures of transverse sections given by Williamson in Megal- 

 ichthys} by Pander in Osteolepis. ^ 



As regards the osteology of the head, the resemblance is 

 exceedingly close between Megalichthys and the Old Eed 

 Saurodipterines, as is at once evident on comparing the figure 

 of the head of Megalichthys given by Agassiz ^ with those of 

 Osteolepis given by himself, by Hugh Miller/ and by Pander. 

 It is not within the scope of the present paper to enter into a 

 minute or even a general account of Saurodipterine cranial 

 osteology ; a few points may, however, be conveniently 

 alluded to. 



1. The polygonal plates covering the ethmoidal region be- 

 tween the frontals and the prsemaxillse are often more or less 

 distinct in Megcdichthys, as in small specimens of Osteolepis ; 

 often they are fused with each other, and with the adjacent bones 

 named above, as seems always to be the case in Diplopterus. 



2. Though Agassiz made a singular mistake with regard 

 to the nasal openings of Megalichthys, he was perfectly 

 correct in recognising the anterior position of the orbit, and 

 in assigning to it a situation exactly corresponding to that in 

 Osteolepis. Professor Young of Glasgow has, however, in a 

 brief notice of a head of Megalichthys belonging to Mr John 

 Smith, Kilwinning, Ayrshire,^ stated that the two outer plates 

 of the posterior half of the cranial shield, which he calls 

 " anterior frontal " and "squamosal" {posterior frontal, and 

 squamosal of the nomenclature adopted by myself), bound 

 the orbit above. This would certainly put the orbits into a 

 position very different to that which they occupy in 

 Osteolepis. By the kindness of Mr Smith, I have had an 



1 Phi]. Trans., 1849, PI. xlii., Fig. 18. 



^ Sanrodipterinen, etc., PI. v.. Fig. 8. 



'•' Poissoiis Fossiles, Atlas, vol. ii.. Pis, 63 and 63«. 



* Footprints of the Creator, Figs. 12-15. 



5 Proc. Geol. Soc, Glasgow, iii., 1868, pp. 202, 203. 



