Shall of the Genus Aulastomatomorplia. 



307 



Tlie liyoiiiaiidihular Iins the usual articulations. 



Tlio oixMcular apparatus consists of the usual four bones. 

 Tlie j)r;voi)erclc is much proh^nged forward to articulate with 

 the quadrate. The sub- and intcropercles are small and 

 linear. The opercle, a very thin triangular bone, bears at its 

 up|)or end a proji'cfing knob, wiiich is seen externally as a 

 well-marked |)rominence halfway between the eye and the 

 Uj)per end of the branchial openint^. 



The lower jaw contains articular angular and dentary 

 bones. 



The upper part of the snout is formed by one long fibrous 

 piece of bone intimately united with the vomer in front and 

 dividing at the base of the snout into two liml)s, between 

 which tlie fore parts of the frontals fit. This long bone repre- 

 sents an ethmoid and two lateral ethmoids ; a suture separating 

 these elements could not be found. 



In the cranium proper the supraoccipital articulates with 

 the frontals and lies between the small parietals, separating 

 them from each other. 



The frontals are not fused in the middle line. 



Skull of Aulastomatomorpha phosphoi-ops. 



