216 Eocene Fossils of the United States. 
I have but one specimen, a cast in indurated clay, without a 
trace of the original shell. remaining upon it. 
Lurrari papyrta. Ovate, very thin and fragile, inflated an- 
teriorly ; surface with concentric sulci, profound on the sides and 
obsolete in the middle, and with numerous interrupted wrinkled 
lines from umbo to base ; anterior end abruptly rounded ; posterior 
side cuneiform, caneinand, gaping ; a slight fold, and nearer the 
end margin, an undulated line from beak to base ; submargin an- 
gular, with a narrow depressed area ah extremity of the valves. 
(Plate I, fig. 8.) 
Lutraria papyria, Con. ; Foss. Shells of Tert. Form. , P- Al. 
Claiborne, Alabama. 
A very rare species and extremely fragile. I have only one 
valve nearly perfect and the fragment of another. The teeth and 
eardinal grooves are remarkably large and profound. 
Macrra. 
The genus Mactra appears to be peculiar to the sorgiry form- 
ations in a fossil state. I have seen no unquestionable species in 
secondary rocks. Deshayes enumerates fifteen fossil species of 
Europe, two of which are in the Paris Eocene. I find three spe- 
cies in the Alabama Eocene, all of which are small. The Mio- 
cene strata of Maryland and Virginia contain the largest known 
species, excepting the recent M. solidissima. 'This formation 
has furnished ten species. Four recent Mactre inhabit the east- 
ern and middle coasts of the Union. One of these, M. lateralis, 
is common in the Gulf of Mexico on many of the Keys, and oe- 
curs fossil in Virginia and North Carolina both in Miocene and 
Post-pliocene deposits. 
This genus has been subdivided by Gray into the genera Spi- 
sula, Scissodesma and Mulinia. Ihave no doubt the anatomi- 
cal structure of the animals of these three groups will, when bet- 
ter known, authorize the genera of this distinguished naturalist. 
Macrra precisa. Triangular, ventricose, umbonial slope an- 
gular, slightly carinated ; posterior slope much depressed, with a 
line somewhat bifid or double from beak to base, and short ob- 
lique prominent lines on the upper portion of the valves; cardinal 
fosset large and profound, the anterior tooth adjoining it trian- 
on with adeep pit on each of the three sides. (Plate Il, 
