EASTMAN: CARBONIFEROUS FISHES FROM THE CENTRAL WEST. 193 
CHEIRODUS M’Coy. 
Cheirodus orbicularis (Newserry and Worrtusn). 
;| (Plate 5, Fig. 52.) 
| 1870. Platysomus orbicularis Newberry and Worthen, Pal. Illinois, Vol. IV., Pl. IIL, 
| Fig. 1. (No description.) 
A number of specimens in the Yale Museum agree with the figure published 
by Newberry and Worthen in having an orbicular body with scales arranged in 
very narrow vertical bands. The identity of these specimens with the type of 
j Platysomus orbicularis is further confirmed by the fact that one of them is so 
| labelled in Newberry’s handwriting. The unsatisfactory illustration of this 
j species induces a suspicion that the type was very imperfectly preserved, in 
which case it is not to be wondered that the authors failed to observe the dorsal 
and ventral peaks exhibited by other specimens. A study of all available 
material enables me to give the following amended definition of this species. 
A small species, attaining a maximum length of about 4.5 em. Trunk 
deep, orbicular in outline, the dorsal margin elevated into a prominent 
peak at about its middle point, and the ventral margin angulated to a some- 
what lesser extent at a point about midway between the branchial apparatus 
and the narrow caudal pedicle. Facial contour of head steep, cranial plates 
granulated and striated; the head with opercular apparatus contained about two 
and one-half times in the total length to the base of the caudal fin. Dorsal 
and anal fins arising at a considerable distance behind the marginal peaks, and 
extending close to the origin of the caudal fin; the latter nearly equilobate, its 
upper lobe with well-developed fulcra, and its width at distal extremity equal- 
ling about one third the maximum depth of trunk. Dorsal fin with fifty or 
more rays, caudal and anal each with a somewhat lesser number. (Paired fins 
not observed. ) 
Scales ornamented externally with faint longitudinal striae and usually one 
longitudinal ridge situated near the anterior border of each scale; attached 
surface coarsely striated, the striae being nearly vertical on the deeper flank- 
scales, but oblique on those situated dorsally and ventrally and in the caudal 
region. Scales of the anterior part of the trunk arranged in nearly vertical 
narrow bands, those toward the tail showing a slight downward and backward 
obliquity, and those at the base of anal fin reflexed forwards toward the ventral 
margin. 
Formation and Locality. — Coal Measures ; Mazon Creek, Illinois. 
VOL. XXXIX. — NO. 7 3 
