195] OSTEOLOGY OF LORICATI—GUTBERLET 25 



HEXAGRAMMOS DECAGRAMMUS 

 The Skull 



The dorsal surface is smooth and more rounded than either Ophidon 

 or Scorpionichthys, on account of the lateral extensions of the pterotic 

 and prootic which makes a broad and flat rather than a deep temporal 

 fossa. The supraoccipital is especially conspicuous as it separates the 

 two parietals and comes to a spine-like point. On each side of the 

 median line the parietals form narrow ridges which extend postero- 

 laterally on the lateral edges of the epiotics and form the mesial edges 

 of the roof of the temporal fossa. The dilatator fossae are shallow 

 grooves in the sphenotic and pterotic bones. They lack foramina. 



The vomer (Figs. 12, 13) in this species has a relatively longer 

 dorsal process than either Ophidon or Scorpionichthys. There is no 

 articular facet on the dorso-anterior edge for the maxilla. Only villi- 

 form teeth are present. 



The ethmoid (Figs. 12, 13) is not grooved but slightly keeled. It 

 has no depressions for the nasal pits and the antero-lateral processes for 

 the support of the nasal bone are similar to those of Ophidon. 



The prefrontals (Figs. 12, 13) have no depressions on the dorso- 

 anterior edge for the nasal pits and have articular facets on the antero- 

 lateral edges for the palatines as in Scorpionichthys. 



The frontals have a smooth dorsal surface which is slightly grooved 

 between the orbits. It is not porous on the ventral surface and possesses 

 a single flange process as in Scorpionichthys, differing from Ophidon 

 and Scorpionichthys in not uniting with the sphenotic to form the pos- 

 terior border of the orbit. As in Scorpionichthys, the sphenotic, in 

 connection with the prootic, forms the facet for the anterior head of 

 the hyomandibular. 



The pterotic is a thin flange-like bone extending postero-ventrally 

 from the sphenotic, thus forming the ventro-lateral boundary of the 

 temporal fossa. 



On the prootic there is a lateral flange-like process ventral to the 

 facets for the hyomandibular; this extends out laterad below the facet 

 for some distance, as in Scorpionichthys. The prootic forms a large 

 part of the anterior facet for the hyomandibular. No special peculi- 

 arities are shown in the arcade or the location of the foramina. 



