On a Chalk Fish fro'm Kansas. 531 



half as long as the pectoral fins — a proportion very di:fferent from 

 that observed in the restored paired fins in the specimens at New 

 York and Lawrence (Kansas). The pelvic bones, which are well 

 shown, are firmly articulated in the middle line at their base, and 

 correspond in shape with those originally ascribed to Portheus by 

 Cope.^ The first fin-ray is much stouter and larger than the others, 

 but it expands a little towards its distal end, and must have been 

 fi.nely divided and articulated at its extremity. The whole fin, in 

 fact, resembles that of another specimen in the British Museum 

 (IS'o. P. 6326) which has already been figured.^ 



Of the median fins, the dorsal and anal are only imperfectly 

 preserved, but the remains suggest that these fins were arranged 

 as in Cliirocentrites ^ and the living Chirocentriis, not as in the 

 restorations at New York and Lawrence (Kansas). The anal fin 

 clearly arises at the beginning of the caudal region, where both the 

 fin-supports and the bases of the fin-rays are seen in nearly undisturbed 

 series. It is uncertain, however, whether this fin extended as a low 

 fringe backwards — it can only be noted that a few displaced short 

 and broad fin-supports in the hinder part of the fossil may have 

 belonged to such an extension. The dorsal fin is represented only 

 by a few supports and imperfect rays at some distance behind the 

 origin of the anal, and it seems probable that if it originally extended 

 further forwards or backwards some traces would be exhibited. 



The deeply forked and powerful caudal fin is already well known, 

 and the new specimen confirms previous descriptions. There is 

 clearly no sudden termination of the vertebral column with a urostyle 

 as in Chirocentrus ; but the five or six hindmost vertebrae form an 

 upturned series, rapidly diminishing in size, as in the Elopines and 

 other primitive teleostean fishes. 



Remains of large and thin scales occur in various parts of both the 

 abdominal and the caudal region, and their outer face often exhibits 

 an irregular coarse tuberculation like that of the opercular bones. 

 The rounded tubercles do not appear to be enamelled. 



The new specimen of Portheus now described, while confirming 

 previous descriptions in many respects, is thus of importance as 

 showing for the first time the relative proportions of the paired fins 

 and the probable true relationship of the dorsal and anal fins. It has 

 already been pointed out that there are striking resemblances between 

 Portheus and Chirocentrites, and the facts now published concerning 

 the fins make it doubtful whether the species belonging to these two 

 categories can any longer be referred to two distinct genera. 



EXPLANATION OP PLATE XVIII. 



Portheus molossus, Cope ; nearly complete trunk, with the head of another 

 individual; about ^ nat. size. Obtained by Mr. Charles H. Sternberg 

 from the Niobrara Chalk of Kansas, U.S.A. (Brit. Mus. No. P. 11125.) 



^ E. D. Cope, Vert. Cret. Form. (Pvep. U.S. Geol. Surv. Territ., vol. ii, 1875), 

 p. 192, fig. 9. 



^ A. S. "Woodward, Foss. Fishes English Chalk (Mon. Pal. Soc, 1907), 

 p. 101, fig. 28. 



3 J. J. Heckel, Denkschr. k.Akad. Wiss. Wien, math. -nat. CZ., vol. i (1850), 

 p. 203. See also A. S. Woodward, Foss. Fishes English Chalk, p. 99, fig. 25. 



