DEVONIAN FAUNAS. 209 
defined sinus, which is usually deeper on the two sides, with a rounded 
elevation in the middle, giving to the shell the appearance of having 
a double sinus. The beak is of moderate prominence, somewhat in- 
curved over the narrow, concave, cardinal area. Brachial valve more 
convex than the pedicle, with a broad, low, ill-defined mesial fold 
toward the front. Surface of both valves marked by fine, radiating 
strie. 
The dimensions of a rather small pedicle valve are: length, 18 mm. ; 
width, 21 mm.; convexity, 5.5mm. Those of an average-sized brachial 
valve are: length, 22 mm.; width, 25 mm.; convexity, 7 mm. 
Remarks.—This species is closely allied to Schizophoria multistriata 
H. of the higher Helderbergian beds, but may be distinguished from 
that species by its more or less conspicuous double sinus in the pedicle 
valve. 
GYPIDULA GALEATA (Dal.). 
Plate XXVIII. Figs: 1-8. 
1859. Pentamerus galeatus Hall, Pal. N. Y., vol. IIL, p. 257, pl. 46, 
figs. 1 a—z, pl. 47, figs. 1 a—m. 
Description.—Shell subglobose, becoming more and more elongate 
with age. Pedicle valve gibbous, becoming exceedingly ventricose in 
the umbonal region in old shells; longitudinally subovate in outline 
when mature, the younger shells often being transversely subelliptical 
in outline; the surface smooth in young indivduals, becoming plicated 
and developing a mesial fold with age; the beak prominent and 
strongly incurved. Internally the dental plates extend forward from 
the margins of the delthyrium, and are united to form a prominent 
spondylium, which is supported by a strong median septum. Brachial 
valve depressed-convex, usually transversely subelliptical in outline, 
but sometimes becoming longer than wide in old age. Surface smooth 
in young shells, and on the umbonal portion of adults, becoming pli- 
cated with age and developing a shallow, indefinite median sinus. 
Surface of both valves marked with low, rounded plications, which 
are more or less variable in number and in prominence, and which do 
not reach to the beak, leaving the umbonal region smooth. Toward 
the beak and upon the umbonal region the concentric lines of growth 
