EASTMAN: CARBONIFEROUS FISHES FROM THE CENTRAL WEST. 20% 
fect 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. rugosus. The lower 
dental plates are more strongly enrolled than the upper, and have more strongly 
marked transverse ridges. Some specimens appear to indicate, also, that the 
fusion between the two parts corresponding to the anterior and posterior den- 
tal 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 
writer exhibits a length along the inner margin of 4.5 cm., and a width along 
the antero-lateral border of 2 cm. 
Formation and Locality. — Keokuk limestone ; Iowa and Ilinois. 
Poecilodus tribulis (St. Jonn and Wortuen). 
1883. Chitonodus tribulis St. John and Worthen, Pal. Illinois, Vol. VIL, p. 117, 
Pl. VIL, Figs. 18-21. 
A specimen belonging to the United States National Museum (Cat. No. 
3496), 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 unlikely that the fragment described by Newberry 
and Worthen as P. convolutus1 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 material. 
Formation and 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 cocanus Newberry. 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. 866, Pl. IL. Fig. 9. 
