SILURIAN FAUNAS. 261 
MOLLUSCOIDEA. 
BRACHIOPODA. 
STROPHEODONTA VARISTRIATA (Con.). 
Plate XXIV., Figs. 13-14. 
See, also, p. 274. 
1859. Strophodonta varistriata Hall, Pal. N. Y., vol. III., p. 180, pl. 
8, figs. 1-16, pl. 16, figs. 1-8. 
Description.—Shell concavo-convex, subcireular, subelliptical or sub- 
quadrangular in outline, length equal to, less or greater than the 
width, hinge-line equaling, less or greater than the width, cardinal 
extremities rounded or angular. Pedicle valve depressed-convex, um- 
bonal region rather prominent, beak extended a little beyond the 
hinge-line, arched over the narrow, cardinal area. Brachial valve con- 
cave or nearly flat. Surface of both valves marked by fine, sharp, 
radiating strie, which vary in size, the stronger ones usually being 
equidistant, with several finer ones between. Crossing the radiate 
markings are much finer, somewhat undulating, concentric lines. 
The dimensions of an average specimen from the Manlius limestone 
are: length, 17 mm.; width, 19 mm. 
Remarks.—Every specimen of the genus Stropheodonta which has 
been observed in the Manlius limestone seems to be referable to this 
variable species. Its most constant characteristic is to be found in 
the surface markings, the proportionate dimensions of the shell being 
different in almost every individual. 
CENTRONELLA? BIPLICATA N. sp. 
Plate XXIV., Figs. 1-8. 
Description.—Shell small, longitudinally subovate in outline, the 
valves subequally convex. Pedicle valve with a sharply-pointed, arched 
beak, the mesial sinus narrow, shallow and extending nearly to the 
beak, but becoming very indistinct or almost obsolete back of the 
