DEVONIAN FAUNAS. 281 
lateral slopes convex, rounding into the posterior region of the valve, 
sometimes bearing a single, subangular plication on each side ad- 
jacent to the mesial fold. Brachial valve transversely subelliptical 
in outline, much less convex than the opposite one, with a more or 
less abruptly-depressed median sinus near the anterior margin, which 
usually contains two well-defined, rounded or subangular plications. 
The surface of both valves, aside from the plications already de- 
scribed, is smooth, or marked only by inconspicuous lines of growth. 
The dimensions of a large pedicle valve are: length, 21 mm.; 
width, 23.5 mm.; convexity, 11.5 mm. Those of a smaller brachial 
valve are: iength, 13.5 mm.; width, 16.5 mm.; convexity, 4 mm. 
Remarks.—This species has only been observed in the upper portion 
of the Coeymans limestone, associated with the variety of G. galeata 
last described. It differs from (. galeata in its much more prominent 
fold of the pedicle valve, which is extended further toward the beak, 
and in its much coarser and more conspicuous subangular plications, 
which are either restricted to the mesial fold and sinus, or to these 
portions of the shell and the immediately adjacent parts of the lateral 
slopes. These characters are constant in all the specimens observed, 
and they show no intermediate forms connecting them with G. 
galeata, and, as they also occur at a somewhat higher geologic horizon 
than the typical galeata, is believed that they are worthy of being dis- 
tinguished as a separate species. 
RHYNCHONELLA SEMIPLICATA (Con.). 
Plate XXIX., Figs. 12-19. 
1859. Rhynchonella semiplicata Hall, Pal. N. Y., vol. I11., p. 224, 
pl. 29, figs. 1 a-o. 
Description.—Shell small, subtriangular or suboval in outline. 
Pedicle valve with a closely-incurved beak, smooth on the umbo and to 
about the middle of the shell; plicated toward the margin, the mesial 
portion depressed toward the front in a rather deep sinus, usually with 
a single, short, median plication. Brachial valve a little more convex 
than the pedicle, smooth posteriorly, with an elevated mesial fold 
toward the front, and plications toward the margin. Both valves 
marked by two or three angular plications on each side of the fold 
