294 TRANSACTIONS OF THE [maR. 15, 



fewer costce and tubercles and the denticles of the posterior face 

 are more remote and more generally turned upward. It is from 

 the same horizon, but is a ver}' distinct species. 



Formation and locality, St. Louis limestone, Alton, Illinois. 

 Collected by Mr. Wm. McAdaras. 



Genus Dactylodus, N. & W. 



In 1866 this genus was defined in the Report of the Geologi- 

 cal Survey of Illinois, Yol. II., p. 33. It was based upon a 

 Petalodont tooth nearly two inches in length and one and a-half 

 in width, of which the crown had the general form of that of 

 Petalodus, but was quite obtuse, was without the enameled folds 

 at the anterior base and the root instead of being spatulate or 

 tongue-shaped as in Petalodus was divided into a number of 

 well-defined rootlets. This tooth was called Dactylodus princeps. 

 Two other species of this genus were also described {D. lohatus 

 and D. ivfiexus), one from the St. Louis limestone and another 

 from the Chester beds having the same general character as D. 

 princeps, but much smaller. Subsequently Mr. Orestes St. John 

 described in Vol. YI. of the Geological Report of Illinois three 

 other species, D. excavatus, D. concavus and D. minimus, all 

 small, two from the St. Louis limestone at Alton and one from 

 the Chester limestone. 



In 1888 Mr. A. von Inostranzeflf described and figured in the 

 " Travaux de la Soci^te des Naturalistes de St. Petersbourg, 

 Yol. XIX.," another species of Dactylodus from the Mountain 

 Limestone of Moscow which he calls D. Bossicus. Meantime 

 (1883), Mr. J. W. Davis had published his paper on " The Fossil 

 Fishes of the Carboniferous Limestone Series of Great Britain,'' 

 in which he gives figures of a species of Dactylodus which he 

 calls Polyrhizodus colei and he considers Dactylodus but a 

 variety of Polyrhizodus. The same view is taken in " The Cata- 

 logue of British Fossil Yertebrata " by Arthur Smith Woodward 

 and Charles Davies Sherborn, London, January, 1890, where, on 

 p. 158, Dactylodus^ N. & W. is described as a synonym of Poly- 

 rhizodus. From this decision I venture to appeal. The species 

 upon which the genus Polyrhizodus was founded by McCoy, 

 P. magnus [Ann. Mag. Nat. Hist. (2), Yol. II., p. 126], has low, 

 broad, arched, obtuse and triturating teeth without cutting edge 

 in which the root is divided into a large number of small radi- 

 cals ; whereas the teeth of which Dactylodus princeps may be 

 considered as the t^^pe are much more nearly like those of Peta- 

 lodus, differing from them in having the edge of the crown less 

 acute and wanting the folds of enamel along the anterior base. 



