IDJESCIRIUPTHOIN Qe By WIEN SIaCIWsS Ole iT ZUCOIDUS 
(UA SECGKNGEI)) INROME WSs, CAIRIBONIUPZIROWS 
Oir IULILION US, 
THE species here described resembles most closely the form 
described by Messrs. Newberry and Worthen as Petalodus destruc- 
tor (Geolog. Survey of Illinois, 1866, Vol. II., p. 35, Pl. II., Fig- 
ures I-3). 
Ine size is Jarste, Une Sxcme lengua loxcime Fo“ eel We 
greatest width of the crown 47™™. It is therefore somewhat 
larger than the teeth figured by the authors named above; but 
the difference is not great, and the teeth of the two species may 
be properly compared. 
The width of the crown of P. securiger is greater than that of 
P. destructor. Yhe height of the crown of the former, measured 
from the apex to the lower border of the enamel band on the 
posterior surface, is exactly that of the tooth figured by Messrs. 
Newberry and Worthen. Nevertheless, the width of the crown 
of the latter specimen must be increased by an eighth of itself in 
order to equal the width of P. securiger. The crown of the latter 
is also less acuminate than that of P. destructor. The lateral 
angles of the two teeth are different. Those of P. destructor ter- 
minate acutely, while those of P. securiger are rounded off. That 
this condition is not due to wear is shown by the fact that the 
enamel folds, as they approach the border of the tooth, become 
directed upward. 
The width of the band of enamel folds is also greater in the 
tooth being described than in P. destructor. In the latter, as we 
find it figured, the width of the band in the middle line of the 
posterior surface is contained in the distance from the band to 
the apex of the tooth four times. In P. secunger the width of 
the band is contained in the distance named only three times. 
In P. destructor the band is described as consisting of five or six 
561 
