ON MEGALICHTHVS 323 



length is a little more than twice the height. The anterior 

 angle is somewhat pointed, the other two are blunt. 



The anterior portion of the head consists, in the adult, of 

 a compound ethmoidal shield or rostrum formed by the 

 synosteosis of the dermal bones of the region. There is a 

 large oval depression or perforation on either side of the 

 shield near its border. The notches in the anterior lateral 

 borders of the shield have been identified with the openings 

 of the external nares. 



Each side of the head is invested by two cheek plates, the 

 larger flanking the post-frontal and squamosal, and the smaller 

 occupying a more lateral position and articulating anteriorly 

 by a straight suture with the maxilla. 



The anterior edge of each large operculum articulates with 

 a much rounded pre-operculum. The opercular fold was very 

 extensive and well protected, and included a sub-operculum 

 and two inferior operculars placed longitudinally and over- 

 lapping each other. 



The mandible is elongate and slender, its long sides being 

 parallel ; what seems to be the articular process has been re- 

 corded as projecting from the middle of the hinder end ; the 

 rami are usually separated in front. Dentary, angular and 

 splenial elements are said to exist in their usual relation to 

 each other. 



The space between the sides of the mandibular rami is 

 occupied by two great elongate plates, the principal jugulars, 

 and a numerous series of lateral pieces, the lateral jugulars. 

 Between the truncated anterior ends of the principal jugulars 

 and the mandibular symphysis is a large azygous rhombic 

 plate, the median jugular. Each of the principal jugulars is 

 about two and a half times as long as broad, and abruptly 

 truncated posteriorly. 



The teeth are conical and pointed, being rounded in trans- 

 verse section. They are folded and striate at the base and 

 smooth above. The maxillary and pre-maxillary teeth are of 



