22 THE GENESEE CONODONTS 
traces of it have been found in these shales which preserve so 
beautifully the delicate tissues of plants and other fragile objects. 
In the present uncertainty, even as to the class of animals 
which bore these teeth, it seems to me advisable to retain Pander’s 
generic names for forms described by him, and to restrict Hinde’s 
genus Polygnathus to those crested crushing or tritoral plates so 
characteristic of his type specimen. 
The species figured herein on Plate III, figs. 3 and 5, differ 
from Centrodus simplex and from the forms illustrated by Hinde, 
in that the base is more arched and rounded, and the teeth are 
shorter and more variable in size. 
From the Conodont bed in Eighteen Mile Creek. 

Fig. 6. Centrodus princeps, Hinde. X 30. 
CENTRODUS, BRINGE ES Eun 
Text Fig. 6. 
1879. Polygnathus princeps. G. J. Hinde, Quart. Journ. Geol. Soc., 
Viol SOON peso. ate DOVE hiom25s 
For the reasons given above, I refer this species to Pander’s 
genus Centrodus. It may even be a variety of his C. simplex, 
differing merely in the more robust and blunted denticles. Fig. 6 
shows one end of a broken specimen; Hinde’s type lacks both 
ends. 
GNATHODUS AMERICANUS, Spec. Nov. 
Pilates Walle ties 
This genus, transitional between the narrow-based_ pectinate 
forms like Prioniodus and the broad-based tuberculated tritoral 
plates of Polygnathus, has hitherto been known by a solitary 
species described by Pander from the marl in the vicinity of 
Moscow. It illustrates the progressive adaptation of the basal 
portion of the plate into a grinding tritor. In Polygnathus this 
transformation is complete, the pectinate ridge either disappear- 
ing or being confined to a crest projecting beyond the tritor. 
