76 BULLETIN OF THE 



bend; in front of this, and between the orbits, it runs abruptly toward the 

 middle of the crown, before reaching which it makes a broad deep curve, car- 

 rying the tube outward to a point opposite the hinder margin of the fontanelle, 

 whence it passes in a nearly straight direction toward the tip of the snout. 

 Before it reaches the latter, it descends to the lower surface. Soon after leav- 

 ing the cranials, the orbitals sink deeply into the tissues of the side of the 

 head; approaching the skin again, each makes a broad curve around the orbit, 

 rising in front above the middle, after which it goes downward to meet the 

 angular, nearly half-way from the eye to the nostril. The angular is rather 

 elongate ; its continuation, the jugular, ends in front of the middle of the first 

 branchial aperture. The sections of the oral are disconnected and detached ; 

 the space separating them from the angular is about equal to that separating 

 them from each other; their length is about two thirds of that of each mandi- 

 ble. At its forward extremity the short orbito-nasal meets the subrostral and 

 the nasal; posteriorly it meets the suborbital and the angular. The nasals are 

 nearly transverse, and would be quite so if not for a decided curve forward 

 at the inner edge of each nostril. A short longitudinal median connects the 

 nasals and the prenasals; the latter have a moderate degree of divergence, and 

 unite with the rostrals. 



Very prominent cranial curves, long occipitals, a shorter suborbital fold 

 in front of the eye, and a more pronounced nasal curve, are among the most 

 patent differences to be noted on this species as compared with Prionodon mil- 

 berti. An approach toward the conditions existing on Cestracion is to be seen 

 in the cranial, rostral, subrostral, and nasal curves, and in the great depth to 

 which the orbitals have sunk in the tissues behind the eye at the side of the 

 head. 



Prionodon. 



Along the trunk, the laterals of Prionodon milberti (Plate VI.) deviate but 

 little from a right line. There is a small degree of curvature behind the occi- 

 put. Opposite the anal the downward bend is hardly perceptible. On the 

 tail, above the anterior portion of the fin, the canal descends hardly half-way 

 to the lower edge of the muscles; it keeps the same relative position as far 

 back as to the hindermost of the vertebrae. 



The aural is transverse, turned back a very little at each end. The occipi- 

 tals reach toward the side, behind the eye ; they are rather short. In the 

 coronal region each cranial makes a long shallow curve inward. From the 

 fontanelle they are nearly direct, converging somewhat ; and they descend 

 some distance behind the end of the snout. Depression of the head has 

 brought orbitals and angulars close together, on the cheek. In front of the 

 orbit, the suborbitals rise higher than the middle of the eye ; the loop formed 

 by them extends more than a diameter in front, and it is about half as far from 

 the orbit to the junction with the angular. The subrostral is long, with a 

 shallow curve around the nostril; the angular is long; the jugular is me- 



