io6 



NEW YORK STATE MUSEUM 



Cranial osteology. The arrangement of dermal roofing plates in the 

 cranial buckler of M. rapheidolabis is shown in the. restoration given 

 herewith and also observable in the head shield represented in plate ii. 



Referring to text figure 24 for 

 comparison, it will be seen that 

 the disposition of these elements 

 corresponds in a general way to 

 the pattern presented by Neocer- 

 atodus. Especially is this true 

 of the median series of plates, 

 the hindermost of which is elon- 

 gated nearly to the same extent 

 as in Homosteus. Other points 

 of agreement between the form 

 under discussion and Homosteus 

 consist in the elongation of the 

 external occipitals, and inclosure 

 of the orbits within the head 

 shield. In more specialized 

 forms, the preorbital and postor- 

 bital plates are merely notched 



Fig. 19 Restoration of Macropetalichthys showing arrangement of _ ■ -n t 1 



cranial plates and course of sensory canals, x^. C ', C^-divided by thc OrbltS, but m MaCrOpetal- 



cen,rals;£0=ex.ernal occipital; ^/-marginal; ^0~median occipi- J^^hthyS, HomOSteUS, and prCSUm- 

 tal ; /'=combined pineal and rostral, corresponding to anterior median "^ 



unpaired plate in Neoceratodus ; PC— preorbital ; /"/O—postorbital ably alsO lu AsterOSteUS, theSC 



two plates unite to form their external border. 



A conspicuous difference between Macropetalichthys and other Anthro- 

 dires, one which has proved a stumbling-block to a correct understanding 

 of the cranial osteology, lies in the fact that the central elements are divided 

 so as to form ^wo small plates on either side immediately back of the preor- 

 bitals ; these are placed one behind the other, the two pairs being separated 

 from contact with each other in the median line by the elongated median 

 occipital plate, very much in the same way as in Neoceratodus. That the 



