A(.!irEX!^EK SCHYPA. 



397 



This shield is nearly circular, has a strongly-elevated keel, terminating back- 

 ward in a hook, which is the hindermost part of the plate. It is contained 

 laterally between the large epiotic plates, behind which about one-half tlie scute 

 projects. The supra-occipital shield rather recalls the form of the same 

 element in Aci/jeuser glaher, but wants the posterior V-shaped notch, and is 

 not so compressed laterally. Its hinder expansion extends back behind the 

 parietal shields, which it divides for nearly half their length, and in front of it 

 is a small distinct ossification, which still further separates the parietals. The 



Fig. 187. — ACIPENSER SCHYPA, IIKAI) SEEN 

 FROM ABOVE. 



ACIPENSER SCHYPA, HEAD SEEN 

 FROM BELOW. 



squamosal is broad, wider than the parietal, and about two-thirds of its length. 

 The frontal plates are somewhat irregular in shape, and do not meet in the 

 median line. The upper nasal aperture is m contact with the outer margin of 

 the frontal scute, while the ethmoid ossifications, three in number, are between 

 the frontals, but do not penetrate far between the parietals. The post-frontal 

 scute is external to the frontal, and forms the upper and hinder border to the 

 orbit. Other shields, some of large size and rayed, cover the space between the 

 nares and the extremity of the snout. The plates are not all in contact, and 

 there are marked interspaces dividing the supra-occipital and parietal from 

 the iirst dorsal and epiotic, between the frontal and post-frontal, and, to a less 



