8o ANNUAL REPORT OF 



Semionotus agassizii (W. C. Redfield). 



(Plate L; Plate II., Figs. 5, 9, 10, 12; Plate III., Figs. 1, 2; Plates VII., VIII.) 



1841. Palceoniscus agassizii, W. C. Redfield, Amer. Journ. Sci., vol. xli., p. 26. 

 1850. Ischypterus agassizii, Sir P. G. Egerton, Quart. Journ. Geol. Soc, vol. 



vi., p. 10. 

 1856. Ischypterus marshi, W. C. Redfield, Proc. Amer. Assoc. Adv. Sci., pt. 



ii., p. 188 (name only). 

 1888. Ischypterus agassizii, J. S. Newberry, Monogr. U. S. Geol. Surv., vol. 



xiv., p. 30, pi. iii., Fig. I. 

 1888. Ischypterus marshi, J. S. Newberry, ibid., p. 28, pi. ii., Fig. 1. 

 1903. Semionotus marshi, G. F. Eaton, Amer. Journ. Sci. [4], vol. xv., p. 264, 



pi. v., Figs. 5, 9, 10, 12; pi. vi., Figs. 1, 2. 



D. 9-10; C. 17; A. 9; P. 12. 



A large and elegantly fusiform species, attaining a total length 

 to- the base of the caudal fin of about 25 cm., in which the length 

 of the head and opercular apparatus is contained three and one- 

 half times. The maximum depth occurs between the paired fins, 

 where the number of longitudinal scale-rows is about 20. Num- 

 ber of transverse scale-rows, counting along the lateral line, about 

 34. Scales universally large and thick. The boat-shaped dorsal 

 ridge-scale covering the base of the dorsal fin anteriorly is rather 

 small, rounded in front and not notched behind, the posterior 

 extremity prolonged instead into a fine point. Fins strong, but 

 relatively short, the caudal rather prominently forked, and with 

 about 17 rays. Dorsal, anal and pectoral fins with about 14 fulcra 

 each, the ventral with about 12. Apparently four dorsal fin-fulcra 

 originate on the dorsal line over the basal supports, the fifth being 

 slightly less than one-half the length of the anterior fin-margin. 



The original description of this species by W. C. Redfield is 

 very meagre, the principal characters noted by him being the 

 stoutness of the fins, and the usually disturbed condition of the 

 dorsal ridge-scales. A more accurate definition was drawn up by 

 John H. Redfield in the report presented by him to the Amer- 

 ican Association of Geologists and Naturalists in 1845, portions 

 of which were published in the Proceedings of the Association for 

 1856, and still others by Professor Newberry, in 1888. Those to 

 whom these sources are not readily accessible may find satisfaction 



