278 



TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



ChcBtodipterus . — The skull (Fig. 152) is aberrantly specialized in the swelling of the 

 ethmoid, frontals and supraoccipital, and in the shortening of the lower jaw. It approaches 

 the scarids in the marked shortening of the dentary and articular, which brings the biting 

 surface near the fulcrum and gives it great power. 



epiof 

 tab 



pf &pare+h 

 na. 



Pomacanthus arcuatus 



Fig. 154. Pomacanthus arcuatus. 



Angelichthys and Pomacanthus. — The deepening and shortening of the head is further 

 accented (Figs. 153, 154). The eyes are smaller and displaced upward and backward 

 beyond the level of the hyomandibular. Reminiscent of Zeus-Wkt. ancestors with highly 

 protrusile mouths are the elongation of the naso-lacrymal region and the upward inclination 

 of the mandible. The power of the bite has been greatly increased by swinging the insertion 

 points of the adductor muscles backward nearly above the quadrate-articular fulcrum and 

 (in Angelichthys) by the development of an incipient joint between the dentary and the 

 articular. Meanwhile the palatoquadrate border has been swung backward past the 

 vertical, so that the lower borders both of the mandible and of the palatopterygoid bar 

 are nearly at right angles to their usual positions. The heavy spikes in the preopercular 

 of these forms are also a sign of relatively high specialization. 



