EASTMAN : CARBONIFEROUS FISHES FROM THE CENTKAL WEST. 193 



CHEIRODUS M'Coy. 

 Cheirodus orbicularis (Newbekuy and Worthen). 



(.Plate 5, Fig. 53.) 



1870. Platysomus orbicularis Newberry and Wortheu, Pal. Illinois, Vol. IV., PI. III., 

 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 

 Pldtysomus orbicularis is further confirmed by the fact that one of them is so 

 labelled in Newberry's handwriting. The unsatisfactory illustration of this 

 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 otlier 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 cm. 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 e([uilobate, 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 obli(iue 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 Localitij. — Coal Measures ; Mazon Creek, Illinois. 



VOL. XXXIX. — NO. 7 3 



