EASTxMAN : CAliBONIFEROUS FISHES FROM THE CENTRAL WEST. 203 



feet material in the hands of St. John and Worthen in 1883 enabled them to 

 add to our knowledge of it. The latter authors were, however, mistaken in their 

 correlation of Deltoptychius plates with the lower dentition of this species, as 

 is proved by the occurrence in the Keokuk limestone of two forms of teeth 

 determinable as the upper and lower dental plates of P. rugosiis. The lower 

 dental plates are more strongly enrolled than the upper, and have more stnmgly 

 marked transverse ridges. Some specimens appear to indicate, also, that the 

 fusion between the two parts corresponding to the anterior and posterior den- 

 tiil plates of Cochliodus is less intimate in the lower than in the upper denti- 

 tion. The largest of the compound upper dental plates examined by the 

 ■\\Titer exhibits a length along the inner margin of 4.5 cm., and a width along 

 the antero-lateral border of 2 cm. 



Forination and Locality. — Keokuk limestone ; Iowa and Illinois. 



Poecilodus tribulis (St. John- and Worthen). 



1883. Chitonodus tribulis St. John and Wortlien, Pal. Illinois, Vol. VII., p. 117, 

 PI. VII., Figs. 18-21. 



A specimen belonging to the United States National Museum (Cat. No. 

 3496 j, and pertaining without doubt to this species, exhibits the characteristic 

 fusion and transverse ribbing of Poecilodus, thus warranting its transfer to 

 that genus. It appears not uub'kely that the fragment described by Newberry 

 and Worthen as P. convolutus ^ falls under the same specific limits as P. tribulis, 

 but we are not prepared to unite the two under one head without the evidence 

 of further materiah 



Formation arid Locality. — Keokuk limestone ; Iowa and Illinois. 



ANTERO-LATERAL AND SYMPHYSIAL TEETH OF UNDETER- 

 MINED COCHLIODONTIDAE. 



Under the provisional generic names of Helodus, Chomatodus, and Venus- 

 todus, a large number of species have been described from the Mississippian 

 series which are held to represent the anterior dentition of various Cochlio- 

 donts, but in only a few instances are they capable of correlation with the 

 principal grinding plates by which these forms are best known. 



In the case of Cochliodus latus Leidy, this species has been definitely ascer- 

 tained to possess at least one, and possibly more than one series of elongated 

 Helodus-like teeth in advance of the large grinding plates in the upper and 

 lower jaws, and also a symphysial series which has received the separate name 

 of Helodus coxmius "iii ewhevvy . Other teeth, which from their resemblance to 

 '■^Helodus coxanus" may be referred to a corresponding position in the mouth, 

 have been described under the names of Chomatodus comptus (^pars) St. J. and 



1 Pal. Illinois, Vol. IV., 1870, p. 30G, PI. II., Fig. 9. 



