312 REV. S. GRAHAM BIRKS 



Megalichthys (hibberti ?) : B11*and B12*, portions of 

 skulls (decorticated). (Plate XIV., fig. i.) 



Mention may also be made of two decorticated specimens 

 Bn* and B12*. 



Bi 1* : Some of the sutures can be traced in this decorticated 

 parietal region of a skull. The path of some of the mucus 

 canals can also be made out. It seems clear that the left 

 squamosal is a separate bone. The reverse side (ventral) of 

 the specimen is much crushed. 



B12* shews the sutures which separate the right squamosal 

 from the parietal of the same side. 



From a number of examples of the anterior portion of the 

 skull it is clear that, whereas in some specimens the so- 

 called " compound-ethmoid," or snout, is divided up by suture 

 into its constituent parts, a complete series shewing every 

 phase from this divided state to a completely fused-up 

 shield can be obtained. In specimens described in this paper 

 and in other examples, as noted, the course of fusion may be 

 indicated thus : — 



B6*. M. hibberti. 

 B5*. M. coccolepis. 

 B20*. M. hibberti. 

 B7*. M. hibberti. 



B13*. M. hibberti; and Dr. Traquair's fig. 3, 

 Proc. Roy. Soc. Edin., viii., 1883-4, p. 67. 



The change is probably ontogenetic, as the examples of 

 M. hibberti exhibiting it would seem to indicate. 



Megalichthys coccolepis : B5*, anterior portion of 

 skull. (Plate XIV., fig. 2.) 



This exceptionally interesting fossil represents the anterior 

 portion of the skull of M. coccolepis. There is some indication 

 that the bones are at a stage where there is a tendency to 

 fusion. 



