EASTMAN : CAKBONIFEROUS FISHES FROM THE CENTRAL WEST. 201 



with IJ. spatulatus. In Plate 4, Fig. 38, is shown a very perfect po-sterior 

 dental plate of the typical form, rather under the average size. Some very 

 large examples have a width along the antero-lateral margin of nearly 6 cm., 

 and in these much worn teeth the coronal contour is decidedly flatter than in 

 immature specimens. 



Messrs. Newberry and Worthen have figured the supposed anterior dental 

 plate belonging to this species,* but the specimen appears to be too strongly 

 enrolled for coadaptation with the antero-lateral margin of the posterior dental 

 plate, and the same criticism applies to the specimen referred by St. John and 

 Worthen ^ to a corresponding position. There is no record of the two prin- 

 cipal dental plates of this species ever having been found in natural associa- 

 tion, and it will require the careful study of much additional material before 

 we can be fully satisfied as to the characters of the anterior components of the 

 dentition. It is to be noticed that the initial coiling is much less marked in 

 the teeth of this species than in most forms of Deltodus and Sandalodus. 



Formation ami Locality. — Burlington, Keokuk, Warsaw, and St. Louis 

 Groups; Iowa and Illinois. 



Deltodus costatus (Newberry and Worthen). 



1870. Cochlmlus costatus Newberry and Worthen, Pal. Illinois, Vol. IV., p. 364, PI. 



III., Fig. 10 {rwn Fig. 12).' 

 1883. CochUodus costatus St. John and Worthen, Op. cit., Vol. VII., p. 167. 



This .species has not been previously reported from a higher horizon than the 

 Burlington division of the Mi-ssissippian, but several examples from the Keokuk 

 lime.stone are preserved in the United States National Museum and in the 

 collections belonging to the State University of Iowa. Very similar teeth also 

 occur in the Warsaw beds, and have been described as Deltodus trilohus by St. 

 John and Worthen.* A tooth of the same general nature is also referred by 

 the same authors to D. occidentalis, and is supposed by them to represent the 

 anterior dental plate belonging to that species.* It is evident that the Warsaw 

 forms last referred to are anterior dental plates, but attempts to correlate them 

 Avith the posterior dental plates of other known forms are necessarily attended 

 with great uncertaint}'. 



Formation aiid Locality. — Burlington and Keokuk Groups ; Iowa. Q. War- 

 saw beds ; Illinois.) 



1 Pal. Illinois, Vol. II., 186G, PI. IX., Fig. 3. 



2 Ibid., Vol. VII., 1883, PI. IX., Fig. 10. 



3 Ibid., Vol. VII., 1883, p. 148, PI. IX., Fig. 8. 



* Pal. Illinois, Vol. VII., 1883, PI. IX., Fig. 10. (Warsaw limestone ; Warsaw, 

 Illinois.) 



