NO. 2177. FOSSIL FISHES IN NATIONAL MUSEUM— EASTMAN. 257 



structure of Petalodonts/ has suggested that the fiii-spines laiown as 

 SticJiacantlius and PJiysonemus (includmg Xystracanthus and Bata- 

 canthus) should be associated on theoretical grounds with the teeth of 

 Polyrliizodus and Petalodus respectively. He also conjectured that 

 the teeth of Petalodus and CtenoptycMus were borne in the mouth of 

 one and the same genus of Palaeozoic sharks. 



Genus POLYRHIZODUS M'Coy. 



Syn. Dactylodus Newberry and Worthen. 



As remarked by Dr. A. S. Woodward in his Catalogue of Fossil 

 Fishes in the British Museum (Part 1, p. 56), "no teeth of this genus 

 havmg been found thus far in natural association, it is impossible to 

 distinguish between specific characters and the variations exliibited 

 by teeth in different parts of a smgle jaw." There is, however, some 

 reason in support of Jaekel's surmise that the teeth of Polyrliizodus 

 are associated in the same jaw with those havmg low and elongate 

 crowns, commonly referred to Chomnfodus. 



POLYRmZODUS CONCAVUS (St. John and Worthen). 



Plate 8, fig. 4. 



The teeth of this species resemble those of P. princeps (the type 

 species of the so-called "Dactylodus^'), but are smaller, and the base 

 of the crown is more strongly arched downward in the middle. A 

 single specimen in the Museum collection, catalogued as No. 8100, is 

 peculiar in showing an appai'ently undivided root. 



Foifnation and locality. — St. Louis Ihnestone (Mississippian) ; near 

 Alton, Illinois (from the Hambach collection). 



POLYRHIZODUS GRANDIS, new species. 



Plate 8, figs. 1, 2. 



Teeth robust and of relatively large size, laterally elongated, with 

 moderately high crown, the base line not much curved on the pos- 

 terior face; the root subdivided mto six or more tumid branches. 



This species is founded upon two specimens m the United States 

 National Museum collection, catalogued as Nos. 8104 and 8116, one 

 of which has the crown very excellently preserved, but lacks a part of 

 the root, and the other shows the latter structure m nearly perfect 

 condition, but has the crown somewhat worn and fractured. 



Probably to this species should be referred certain low and elongate 

 CTiomatodus-YikQ teeth occurrmg in the same formation, by analogy 

 with the association of two very similar types of teeth belonging to 

 P. concavus Trautschold, from the Russian Coal Measures. This is in 



1 Jaekel, Otto, Ueber die Organisation der Petalodonten. Zeitschr. Deutsch. Geol. Ges., vol. 51, 1899, 

 pp. 258-298. 



65008°— Proc,N.M.vol.52— 17 17 



