274 
Aug. F. Foerste 
The number of radiating plications appears to vary considerably. 
If only those shells are selected in which both the cardinal margin 
and the anterior face are well exposed, then 45, 46, or 47 radiating 
plications are very frequent. However, specimens occur in which 
the number of plications is as great as 55. In the specimens with 
45 radiating plications, these plications are distinctly broader 
than the intervening grooves; in those with 55 plications, the 
width of the latter exceeds that of the intervening grooves only 
slightly, if at all. Since the number of plications is considered 
as of diagnostic value in the genus Byssonychia, an attempt was 
made to discriminate two species among these Lorraine forms 
from Pulaski, but without success. Some of the forms with the 
greater number of plications are slightly more erect and somewhat 
longer along the hinge-line, but others have the larger number of 
plications without differing in form or outline from those speci- 
mens in which the number of plications is smaller, and, of course, 
specimens with intermediate numbers occur. At Pulaski, speci- 
mens with about 45 plications are rather abundant both in the 
gorge south and southwest of the town, and also along the river 
banks eastward, as far as the railroad bridge. Specimens with 55 
plications occur, associated with the others, at the Trinucleus 
horizon, several hundred yards west of the railroad bridge. In 
none of the specimens does the posterior margin meet the cardinal 
line as in the illustration of Byssonychia praecursa, Ulrich, on 
plate 45 of the Geology of Ohio, vol. VII. The angle is much more 
obtuse, the posterior margin, in most specimens, rounding almost 
gradually into the cardinal outline. 
The statement by Hall that Byssonychia radiata has 25 to 40 
plications probably indicates that he had specimens with 45 plica- 
tions in his possession, those on the anterior face not being well 
exposed. The specimen illustrated by Fig. 4a, on plate 80, of 
the Paleontology of New York, vol. I, was examined for me very 
obligingly by Dr. Chester A. Reeds, and found to possess 48 
radiating plications. The original of Fig. 46 exposes 42 plica- 
tions and about 6 are still covered by rock. In 4/, 50 plications 
are certain. In 4c, 28 plications are visible but additional ones 
are present but not exposed. See Fig. 12c, pi. Ill, this Bulletin. 
The vertical range of Byssonychia radiata is considerable. It 
occurs at Bennett bridge, and also half a mile eastward up the 
river, and the same distance west of the Salmon River Falls. 
