G. F. Eaton — Collection of Triassic Fishes at Yale. 263 



originate on the dorsal line over basal supports. The 5th dor- 

 sal fulcrum has its origin adjacent to that of the 1st ray, and 

 is about equal in length to one-half the anterior margin of 

 the fin. 



Pectoral fins show, on the superior surface, about 10 fulcra, 

 long and slender, and not widely divergent from the rays, 

 which are about 10 in number (Plate V, fig. 2). 



Ventral fins show, on the superior surface, about 10 fulcra. 



Caudal fin has about 15 rays. 



The best preserved specimens are a little less than four times 

 as long as deep, the maximum depth being midway between 

 head and dorsal fin, where the oblique scale-row comprises 

 about 20 scales. Horizontal scale-row along lateral line com- 

 prises about 33 scales. 



The deepest scales are in the 4th row behind the clavicular 

 arch ; these are twice as deep as long.* Scales of the anterior 

 caudal region are nearly equilateral. With the exception of 

 the scales of the lateral line, the anterior flank scales generally 

 have the postero-inferior angles slightly rounded (Plate V, 

 fig. 3), and the posterior flank scales have the postero-inferior 

 angles produced into single points (Plate V, fig. 4). In rare 

 and doubtful cases, the posterior borders of the flank scales 

 may be slightly irregular, but never to the extent commonly 

 seen in S. micropterus. 



Semionotus micropterus Newberry. 



Ischypterus micropterus J. S. Newberry, 1888, Mon. U. S. Geol. Surv., 

 No. xiv. 



One of the fishes placed by Dr. Woodward in his list of 

 doubtful species is S. micropterus. It is encouraging to find 

 that good specimens, not accessible when his Catalogue was 

 compiled, now make it possible to describe this species more 

 fully and to separate it from other forms by the characters of 

 its fins and scales, and not solely by its contour. This species 

 may be described as follows : 



S. micropterus, attaining a length of 10 inches and a depth 

 of 3 inches. 



Relative position and size of fins about the same as in 

 S.fultus. 



Dorsal fin fulcra about 14, rays about 9 (Plate V, fig. 13). 



Anal fin fulcra about 14, rays about 9. 



Dorsal and anal fin fulcra relatively shorter than in S. fultus. 

 Apparently 3 dorsal fulcra originate on the dorsal line over 

 basal supports. The 5th dorsal fulcrum has its origin on the 

 anterior margin of the 1st ray, at a point considerably removed 



* These and similar measurements refer to the exposed portion of the 

 scales, not to actual dimensions. 



