LEIOGNATHUS 11 



is a deep conical cavity with its apex pointed forward, just as in the 

 genus Gnathanodon and in several members of the family Scombridae, 

 only the myodome does not open into its side, as it does in the Scombri- 

 dse. The parasphenoid extends a little behind the front of the posterior 

 opening to the myodome in a little sliver of bone on each side, but it 

 does not reach nearly to the basioccipital condyle. A broad wing is 

 developed upwards along the prootic on each side of the myodome and 

 is strengthened by a lateral ridge continuous with a sharp thin ridge on 

 the prootic and the outstanding wing of the sphenotic. As the prootics 

 and the lower edges of the basioccipital end abruptly against the para- 

 sphenoid, without curving inward at all toward each other, the parasphe- 

 noid forms the entire lower floor of the myodome. 



Through the lateral wing of the prootic is a rather long tunnel 

 the trigemino-facialis recess, running from the middle of the preorbi- 

 tal surface of the bone forward, and opening on the orbital surface. A 

 foramen opens into this recess at about its middle on the postorbital 

 surface just below the articular cup of the hyomandibular. 



The alisphenoids meet and divide the anterior opening of the brain 

 case into two parts a lower round part, and an upper, much larger, 

 triangular part. 



Bordering the posterior half of the lower opening is the basisphe- 

 noid. It is connected with the prootic roof of the myodome for its full 

 width without an opening between. It sends down a long process to the 

 parasphenoid. 



The sphenotic stands outward in a very prominent lateral wing be- 

 hind the eye, and is continuous with the frontal supraorbital border. 

 To its outer edge is attached one of the suborbital sensory tube bones, 

 which reaches upward to the frontal. 



The opisthotic is almost wholly on the inferior surface of the cra- 

 nium, though a portion of its thickened posterior end is visible from 

 above. It covers the pterotic-exoccipital suture, and no part of it is 

 interposed between the pterotic and exoccipital. The broad lower limb of 

 the posttemporal is firmly attached to it without the intervention of a 

 ligament. 



The parietals are widely separated by both the supraoccipital and 

 the posterior points of the frontal which project backwards. They are 

 situated just above and anterior to the epiotics. Each is in outline an 

 irregularly round bone, and is traversed by a sharp wing running 

 from just behind its middle upward to where the frontal joins the su- 

 praoccipital ridge. 



