OF DENISON UNIVERSITY. 
25 
curves somewhat abruptly at its upper third, the posterior margin is 
straight. The ears are acute and depressed, while the beak is acute 
and somewhat elevated. There seem to be indications of the hinge 
ridge or furrow peculiar to this genus. Markings obscure, but appa- 
rently consisting of few radiating and many faint concentric lines. 
Length, the greatest width. Hinge somewhat over the great- 
est width. 
Genus Aviculopecten. 
The literature at command makes an attempt to study the numer- 
ous members of this genus rather unprofitable, but in as much as sev- 
eral have been figured we may briefly allude to them. 
v^viculopecteib hertzeri, Meek. 
(Plate I, Figs. 5 and 10.) 
Specimens corresponding in size and form to Meek’s type, are 
numerous, and occasionally one encounters the same shell of double 
the usual size, but retaining the characteristic marking. This species 
may be recognized by the close thread-like concentric and radiating 
lining producing a peculiar textile structure. This may be seen from the 
inside of the shell also. In the smaller specimens seen the shell sculp- 
ture is somewhat different. The entire shell is covered by strong radi- 
ating costae in pairs, the costae being closely crowded but separated by 
deeply impressed grooves between the pairs. These radiating lines 
are crossed by very fine and numerous concentric striations. The 
pairs tend also to again bifurcate toward the lower margin. This 
dichotomous arrangement of the very strong radiating ribs seems to 
distinguish this form constantly, though it may be, as at first supposed, 
the younger variety of A. hertzeri. 
Aviculopecten? sp? 
(Plate III, Fig. 18.) 
The shell figured resembles A ? sublobatus, Phillips, but is still 
more elongate. It may be that the shell has suffered some distortion, 
though there little indication of it, and until other specimens are seen 
it will not do to rely too much on the figure. The left (?) valve fig- 
