ceed 
strengthened by an elevated carina of a horse-shoe shape and 
extending in front two-thirds of the length of the valve. The 
dorsum is elevated, somewhat conical, a ridge extending from 
the anterior edge to the middle and ending in an acute apex. 
From the apex the, valve slopes regularly to the margin. The 
last seven valves have on either side of the ridge and projecting 
anteriorly from the lateral areas an accessory plate, which when 
In the roof of the Danville coal. ; “2 
2. CO. parvus, n.s. Anterior valve semicircular conical. A 
,pointing posteriorly, sloping regularly to the margin. Made 
valves acutely subrhomboidal, scooped in front, sharp bas 
dorsum elevated, terminating posteriorly in an acute apex. 
terior valve semicircular behind, abrupt in front, rising into an 
acute ridge, extending to the middle of the valve, terminating 
an acute apex, from which the valve slopes to the margin, bis 
is thickened and turned up. Accessory plates more broadly 
rounded than in the preceding species. Surface under. the glass, 
Is minutely granulated. 
ength: plates, 0-1 of an inch: shell 1-2 inches. 
Archimides limestone, Bergen Hill, Ind. 
Appendix. ig 
Avievta (Klein). —1, A. orbiculus, ns, Shell cireular, fat 
tened, thin, attenuated at the margins. Hinge-line straig bal 
half the width of the shell. Auricles small, corrugated, be 
small, scarcely prominent, surface smooth. 
a aa : height 0°75 of an inch. Width, ditto. 
tower coal series of the Appalachian system, at Summit, 
Slana Co., Ohio. In the upper black shales at Springfiel 
# 
