652 BASHFORD DEAN, 



is raaking its appearance as distinctly a paired structure. The cerato- 

 hyals, CA., can be clearly made out passing from the jaw hinge to 

 the hypobranchial region ; a slight depression immediately behind the 

 mandibular Symphysis indicates the uplifting of the glossohyal; im- 

 mediately behind, its posterior border slightly uplifted, the jugular 

 may be seen to consist of two pairs of elements. These, however, 

 are already closely apposed, forming together the shield-shaped mass, 

 whose growth and dermal calcification will shortly give it the ap- 

 pearance of an unpaired structure. It follows, therefore, that there 

 is no need of regarding the jugular plate of Ämia as having had an 

 independent origin from the paired structures of the early Teleostomes, 

 — although one must acknowledge that it is decidedly remarkable 

 that so ancient a feature of dermal armoring should have been re- 

 tained in this most modern of Ganoids, while lost in the gar-pikes 

 and sturgeons; its function must obviously have been an important 

 one to have caused it not merely to be retained but to become en- 

 larged and specialized. Its relation to the sensory canals of the 

 lateral line System, as shown by Allis, is noteworthy in this con- 

 nection. 



Larva of about the fifteenth day (PI. 10, Fig. 20; 

 ventral aspect PI. 10, Fig. 21). 



A great advance in the conditions of the fins is apparent in this 

 stage, and a corresponding growth in the breadth and thickness of the 

 hinder trunk. The length of the dorsal fin is clearly indicated; the 

 line of the dorsal fin-rays, r., with their corresponding row of basal 

 supporting elements, &., terminate abruptly at a position which will 

 mark the hindmost point of the dorsal fin of the adult. There is no 

 trace of a series of larval fin Supports surrounding the protocercal 

 tail tip to connect the dorsal fin with the definitive caudal, as 

 would naturally be supposed, if this, aecording to Shufeldt, were 

 the ancestral condition in Ämia (cf. U. S. Fish Commission Rep., 

 1883, Explanation of fig. 25). In the various fins the number of 

 radialia which may now be counted are as follows : dorsal 57, caudal 

 20, anal 10, anterior anal — a larval element as yet persistent — 0, 

 ventral (?), pectoral 15. Comparison of these numbers and those 

 of additional larval stages with the adult's leads to the conclusion 



1) In the opposite table a general view may be had of the 

 numerical increase (approximate orily — i. e., as counted in surface 

 view in single specimens) in radial fin supports at successive stages. 



