? SILURIAN FAUNAS. 241 
the Helderbergian specimens, the more coarsely plicated individuals 
from the higher beds being similar to the Decker Ferry specimens. 
These specimens seem also not to grow as large as those in the Hel- 
derbergian fauna. 
WHITFIELDELLA NUCLEOLATA (Hall). 
Plate XXI., Figs. 38-40. 
1852. Atrypa nucleolata Hall, Pal. N. Y., vol. IL., p. 328, pl. 74, figs. 
10 a—m. 
1897. Whitfieldella (?) nucleolata Schuchert, Bull. U. S. Geol. 
Surv., No. 87, p. 461. 
Description—Shell subglobose, small, subovate in outline, a little 
longer than wide, rostrate posteriorly, slightly flattened or emarginate 
in front. Pedicle valve with a prominent, incurved beak, slightly 
flattened or sinuate along the median line. Brachial valve shghtly 
less convex than the pedicle, most prominent posterior to the middle, 
usually flattened or slightly sinuate along the median line towards the 
margin. Surface of both valves smooth or marked only by incon- 
spicuous, concentric lines of growth. 
The dimensions of an average specimen are: length, 7 mm.:; width, 
6.5 mm.; thickness, 5 mm. 
MOLLUSCA. 
PELECYPODA. 
EDMONDIA? DECKERENSIS N. sp. 
Plate XXII., Figs. 6-7. 
Description.—Shell subovate in outline, height about three-fourths 
the length; the beak rather small, situated about one-fifth the length 
of the shell from the anterior end; hinge-line arcuate. Anterior mar- 
gin rather sharply rounded, the ventral and posterior margins broadly 
rounded; the curve from the centre of the ventral margin to the pos- 
terior extremity of the hinge-line being nearly a semi-circle. The 
16 
