1889.] 
317 
[Foerste. 
two outer plications of the mesial fold are less elevated than the 
other two plications so that the fold appears rounded. In other 
shells it projects boldly from the surface of the shell although the 
elevation above the lateral lobes attained is not likely to exceed 
1.8 mm. for specimens 11 mm. long. The mesial sinus is always 
well-defined, but not very deep. Occasionally three plications occur 
in the dorsal fold, and two in the ventral sinus. From five to six 
plications occur on the lateral lobes. The character of these plica- 
tions is somewhat variable, in some specimens being quite angular, 
in others being broad, flat, and very much rounded. All grada- 
tions between these forms occur. Casts of the exterior of the shells 
show occasionally traces of concentric striae, but these are usually 
obsolete. It must be remembered, however, that even fine sand- 
stone is not the best element for the preservation of the fine con- 
centric striae of most species of Rhynchonella. 
The beak of the ventral valve in case of the more flattened spec- 
imens is apt to be more erect, and although curved does not cover 
up the beak of the dorsal. In the more obese specimens, how- 
ever the ventral beak is strongly curved, almost, and frequently 
entirely, covering the beak of the dorsal valve. 
Direct comparison with Canadian specimens of Rhynchonella 
Janea from Anticosti, having the concentric striae usually obsolete, 
show no appreciable differences between it and the Alabama spec- 
imens, although the Anticosti form occurs at a somewhat lower 
horizon. 
It is not so well determined, however, that this species is distinct 
from Rhynchonella neglecta , Hall, of the Clinton group. The only 
appreciable difference seems to be the greater development of the 
mesial fold and sinus in Rhynchonella Janea. As species of Rhyn- 
chonella are now defined, it is to be doubted if the Clinton types of 
Rhynchonella neglecta, Hall, will not come to be distinguished from 
the Niagara species, and since the Clinton types were described 
first, it is presumed that the Niagara forms will receive a new name. 
In the case of the species next to be described, however, the Niag- 
ara forms are taken as the type of the species as is customary, for 
some reason unknown to us, in American literature. 
Rhynchonella. neglecta, Hall. 
(plate VI, FIG. 12.) 
This species occurs in moderate abundance in the Clinton at 
Hanover, Indiana. On direct comparison with New York Niagara 
