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ag Description of New Species of Fossils. 259 
summer of 1875. They were found in considerable numbers among the 
leaves under a little clump of trees in a corn field. The spot was 
afterward cleared and plowed over, so that this rare shell has become 
extinct in that locality. The above description differs somewhat from 
Bland’s original description of the H. stignificans, but the shell we 
found is undoubtedly the same. 
DESCRIPTION OF NEW SPECIES OF FOSSILS. 
By S. A. Mitirr, Esq. 
TRIGONIA STIEBELI, 0. sp. 
(Plate VI., fig. 1, view of the left valve; fig. la, cardinal view, the right valve of the 
specimen is unnaturally inflated.) 
The shell of this species is very large, subquadrate in outline, and 
only moderately inflated. The length is a little more than the 
height. The anterior end extends but slightly beyond the beaks, and 
is gently rounded below. Nolunule. The beaks are small, anterior, 
slightly incurved, and raised but little above the hinge line. The hinge 
line is straight and gently sloping backward. The posterior end is 
subtruncate above, and rounded into the base below. The base line 
curves up more rapidly toward the anterior end than behind. 
About twenty ribs rise from the upper margin behind the beaks, 
and passing down and curving forward reach the anterior end and 
basal border. These ribs are very strongly nodulose from the umbonal 
slope to the anterior and basal margins, and more finely nodulose above 
the umbonal slope, and between it and the upper margin, though a 
line of nodules marks the superior border behind the beaks which 
increase in size toward the posterior end, and another line is directed 
backward midway between the latter and the umbonal slope. The 
entire surface of the shell is covered by fine sub-imbricating lines. 
The specimen illustrated and described was collected by Bernard O. 
Stiebel, a naturalist, in whose honor I have proposed the specific name, 
from strata supposed to be of Cretaceous age, in the southeastern part 
of Arizona. The author, however, is directly indebted to Prof. Ralph 
Colvin, through whose kindness the specimen was furnished for defini- 
tion and who also presented it to him. 
