
654 The American Naturalist. [July, 
On Some New Fishes from South Dakota.—The Rev. 
D. S. McCaslin and the Rev. Wm. M. Blackburn have sent me some 
specimens of fossil fishes obtained by the latter gentleman from the 
Ree Hills in South Dakota. They are preserved on slabs of a soft, 
chalky rock, and are in pretty good preservation. The age of the 
horizon has not yet been determined. It is overlaid, according to 
Mr. Blackburn, by a thin layer of glacial drift. There are five spe- 
cies, all new to science. I describe them below, and reserve reflections 
as to their probable geologic age until their characters have been 
pointed out. 
GEPHYRURA CONCENTRICA, gen. et sp. nov, Isospondylorum vel 
Haplomorum.—Char. gen.—Mouth small, the superior border formed 
by the premaxillary, the maxillary apparently not contributing ; no 
teeth. Branchiostegal rays six, or probably seven. Dorsal fin median 
in position, short, originating above a point just posterior to the 
origin of the ventrals, and extending to a point above the anal fin- 
Vertebre keeled, the last not modified by the development of hypural 
bones, but terminating abruptly, or gephyrocercal (Ryder). Caudal 
fin normal, and not elongate. Scales cycloid, with strong concentric 
grooves, and a few proximal radii crossing them. No lateral line dis- 
cernible, Fins without conspicuous spines, a 
Char. specif.—The only specimen is broken vertically across the 
middle, and the posterior half shifted so as to lie immediately below its 
proper position. It appears that little or no part of the fish has been 
lost. Radii, P.9; D. 9; C. 6-16-8; A. II 11. V. 1-6; vertebre, 
to-18. Scales in twelve longitudinal rows between dorsal and ventral 
fins, and equal in number to the vertebrze on the longitudinal line, or 
twenty-eight. Head covered with scales ; five in a vertical line on, 
the operculum. The dorsal, pectoral, and ventral fins are rather 
small. The caudal fin is probably not much forked, if at all. The 
orbit is large, but its outlines are not well preserved. The head enters 
the total length four and a quarter times to the base of the caudal fin- 
rays, and slightly exceeds the depth at the ventral fins. Total length, 
1mm. ; do. of head, 15 mm.; do. to base of ventral fin, 24.5 mm. ; 
do. to base of anal fin, 30 mm. ; depth at ventrals, 14 mm. ; depth at 
caudal peduncle, 6 mm, 
This fish may belong to the Cyprinodontide. It is peculiar in the 
absence of the hypural bones, . 



