96 THE GENESEE CONODONTS 
The upper surface of Polygnathus tuberculatus is convex and 
sculptured with tubercules and rugosities which have a tendency 
to radiate from the center of the plate. In my specimens there 
is hardly ever a prolonged central keel. More often it occurs 
only at one end of the plate, beyond which it projects from a 
deep notch, as a’ stout process, armed with sharp teeth. On 
either side of this notch 1s a narrow basal lobe, each with an 
oblique nodose ridge. 
Conodont bed, Eighteen Mile Creek. 

Fig. 7. Polygnathus rotundilobus, Bryant. Associated with fish plate 
«x 14. 
POLYGNATHUS ROLUNDIEOBUS Sree Nov 
Plate eli eines Oni dkexcternlones 
1879. Polygnathus tuberculatus, G. J. Hinde (in part), Quar. Jour. 
Geol. Soc., Vol. XXXV, p. 366, Plate XVII, fig. 10. 
This is a robust but graceful form. The main plate is roughly 
triangular with rounded lateral lobes. The tritoral surface is 
convex and is armed with clusters of tall, conical tubercules, 
while the underside is smooth and polished, with the usual central 
diamond-shaped pit, from which a furrow extends beneath the 
produced keel. This keel bears upon its summit a few very 
stout, compressed teeth. I have figured various aspects of these 
