THE HEAD OF OSTEOLEPIS. 



185 



recurved ventral border of the shield. At the hinder corner of the skull, 

 between the squamosal, tabulare and supratemporal, is a small triangular 

 plate, figured by Pander and Gregory but not by Watson and Day. This 

 scale-like plate seems to have been attached to the supratemporal and possibly 

 overhung a spiracular opening. Below it passed the head of the large 

 curved hyomandibular (traces of which can often be seen) to articulate with 

 the supratemporal. 



The lateral aspect of the head is by far the most difficult to interpret since 

 the bones are here almost always much crushed and displaced, especially 

 near the articulation of the jaws. . Nevertheless, there can be no doubt of the 

 existence of a large curved squamosal covering the whole of the cheek behind 

 the postorbital and jugal. It has been well figured by Watson and Day, but 

 Pander seems to have considered that it consisted of three plates, being partly 

 misled by the curved superficial groove shown in figure 1 B. The squamosal 

 reaches down to the articulation of the jaws, covering the quadrate region. 

 Just behind its hinder edge, and overlying the end of the hyomandibular, is 

 a small plate, the preopercular. This element is not figured by "Watson and 

 Day, but is possibly the one drawn by Pander and designated quadratojugal 



Fig. 4. 



Fig. 5. 



Fig. 4. Diagram of the bones of the skull of Osteolepis macrolepidotus, from Pander. 

 Fig. o. Restoration of head of Osteolepis microlepidotus, from Pander. 



by Gregory. If so, its true position has not been correctly determined by 

 these authors. For a long time I doubted the existence of this separate 

 element which is almost always considerably displaced ; but after very careful 

 examination of the most favourable material was finally convinced of its 

 presence. The conspicuous large opercular bones pass ventrally into a series 

 of lateral gular or bramchiostegal plates, which end in a pointed anterior 

 element wedged in between the ventral gular anil the lower jaw. Pander's 

 restoration of the lower jaw appears to me much more correct than that of 

 Watson and Day. No trace could be found of the series of infradentaries 

 figured by the latter authors. The dentary and angular are obvious ; an 

 'opercular' or prearticular plate seems to have covered part of the inner 



