262 PALEOZOIC PALEONTOLOGY. 
middle of the shell; it is limited on each side by a single, low, rounded 
plication, which is not conspicuous, except near the anterior margin. 
The brachial valve with a low, rounded, median fold near the anterior 
margin, bounded by a shallow, rounded furrow on each side and not 
rising above the general surface of the valve. Internally it bears a 
short, Centronella-hke brachidium. Besides the two plications which 
bound the fold and sinus, each valve, in the larger individuals, is 
marked by one or two additional, extremely-faint plications near the 
margin on each side and by more or less indistinct lines of growth. 
The dimensions of a rather large specimen are: length, 4.75 mm. ; 
width, 3.5 mm.; thickness, 2 mm. 
Remarks.—This little shell is probably not a member of the genus 
Centronella, but its brachidium, as seen in transparent or translucent 
specimens, is similar to the loop of this genus, and therefore it is 
placed here provisionally. In external form the shell differs materially 
from the typical members of the genus, and, in fact, it differs in ex-_ 
ternal form from all the genera of the family Centronellide. With a 
more perfect understanding of the loop of this shell, it is entirely 
probable that it would constitute the type of a new genus. 
In certain layers of the Manlius limestone in the Nearpass quarry 
this little shell occurs in great numbers, many of which can be removed 
from the rock in perfect condition. In the smaller or younger speci- 
mens of the species the two plications near the front margin are very 
faint or entirely obsolete, but in full-grown individuals they can always 
be detected. 
SPIRIFER VANUXEMI Hall. 
Plate XXIV., Figs. 9-12. 
1859. Spirifer vanuzemi Hall, Pal. N. Y., vol. IIL, p. 198, pl 8) 
figs. 17-23. 
Description.—Shell small, wider than long, hinge-line a little shorter 
than the greatest width of the shell, cardinal extremities rounded. 
Pedicle valve strongly convex, beak elevated and arched over the con- 
cave, ill-defined cardinal area, mesial sinus rounded, not much stronger 
than the rounded furrows on the sides. Brachial valve less convex 
than the pedicle, with a rounded, mesial fold, slightly flattened on the 
top. Surface of each valve marked by from two to four broadly- 
