GREGORY: FISH SKULLS 



183 



since the two genera plainly belong to different orders, which must have begun to diverge 

 perhaps even before the Lower Jurassic. The skull of Erythrinus in the side and top views 

 resembles that of Amia in being covered with broad flat bony plates of somewhat similar 

 sculpturing, but in Erythrinus the epiotic seems to be secondarily reduced in size and the 

 pterotic is much crowded by a row of three bones which include the dermosphenotic and 

 what appear to be posterior extensions of the dermosphenotic, or perhaps anterior exten- 

 sions of the scale bone or so-called supratemporal. The nasals (Fig. 68), as in most teleosts 

 are widely separated by the large and progressive mesethmoid (dermethmoid) but they 

 might be conceived to be in a transitional stage in which they were withdrawing from the 

 mid-line toward the lateral borders of the blunt snout. 



dn.. 



Erythrinus 



Fig. 68. Erythrinus unitaniatus. Top view. 



As the eye is relatively far forward and of only moderate size, the cheek plates are 

 very large and simulate those of Amia. The lacrymal, oh the other hand, is small and I 

 find no trace of an adnasal in this genus although there seems to be one in Distichodus (Fig. 

 65). The nasal has much the position and appearance of the nasal of the Semionotids 

 save that it is now overspread dorsally by the premaxilla and the dermethmoid. Perhaps 

 the greatest objection to Sagemehl's idea of a close relationship between the primitive 

 characins and Amia lies in the fact that the former possess a fully developed Weberian 

 apparatus and that no known member of the amioid group shows the slightest tendency 

 toward the development of these highly complex ossicles. 



