178 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
A single tooth of this species is described by St. John from the Missourian 
near Nebraska City, and another is figured by St. John and Worthen from a 
corresponding horizon in Adams County, Iowa. Professor Barbour has also 
obtained a solitary example from the Atchison shales of Peru, Nebraska. 
Formation and Locality. — Missourian ; Iowa and Nebraska. 
Ctenoptychius occidentalis (St. Joun and WortHey). 
(Plate 2, Fig. 10.) 
1875. Ctenopetalus occidentalis St. John and Worthen, Pal. Illinois, Vol. VI., p. 401, 
Pl. XIL, Fig. 14. 
This species is founded on very delicate, gently arched teeth with relatively 
few (10-12) and obtuse coronal serrations, the broad basal band on the outer 
face being sharply set off from the exposed portion of the crown. The two 
examples known to the authors of this species were derived from the Lower 
Coal Measures in the vicinity of Fort Dodge, Iowa. The trivial title of 
occidentalis was bestowed by the same authors upon still another species of 
Ctenoptychius, which they placed in the now obsolete genus ‘ Harpacodus.” 
The form occurs in the St. Louis limestone of Illinois and Missouri, and so 
closely resembles C. compactus (St. J. and W.) from the Chester Group, that 
we have no hesitation in uniting it with that species. A single detached 
crown of C. occidentalis, somewhat weathered, was obtained by Professor 
Barbour from the Atchison shales of Richfield, Nebraska. 
Formation and Locality. — Productive Coal Measures; Iowa. Missourian; 
Nebraska. 
PERIPRISTIDAE. 
PERIPRISTIS Sr. Jonn. 
Proc. Amer. Phil. Soc., Vol. XI., 1870, p. 434. — 
Hoplodus R. Etheridge, jun., Geol. Mag. (2), Vol. IL., 1875, p. 243. 
Diodontopsodus J. W. Davis, Brit. Assoc. Rept., 1881, p. 646. 
Pristodus J. W. Davis (ex Agassiz MS.), Trans. Roy. Dublin Soc. (2), Vol. L, 
18838, p. 519. 
Peripristis semicircularis (NewBerry and WorTHEn). 
(Plate 2, Figs. 5-7; Plate 3, Fig. 25.) 
1866, Ctenoptychius semicircularis Newberry and Worthen, Pal. Illinois, Vol. IL., 
p..42; El. AV .; Big: 18. 
1870. Peripristis semicircularis O. H. St. John, Proc. Amer. Phil. Soc., Vol. XI., 
p. 4384. 
