Rathbun.] 32 [May 15, 
A few specimens of Retzia, which probably represent only a variety 
of R. Wardiana, are contained in the collections made on the Rios 
Mecurt and Curud. They agree in form with the Ereré specimens, 
but the plications on the shells from the two former localities are 
slightly larger, and fewer in number, there being about twelve on 
each valve. 
Devonian sandstone, Ereré. (Morgan Exs., 1870 and ’71; Geol. 
Comm.,’76.) Rios Mzcurti and Curud. (Geol. Comm., 1876.) 
Rhynchonella ererensis, sp. nov. 
Shell of large size, suborbicular in shape and marked with promi- 
nent, separated plications; length only very slightly greater than the 
width; thickness through the two valves apparently nearly equal to 
the width. 
Dorsal valve subcircular in outline with a slightly projecting, 
sharply pointed beak ; cardinal margins moderately concave and ex- 
tending far forward. Viewed from the side, the surface rises rapidly 
upward from the beak, along the median line, in quite a regular 
curve for about one-half the length, whence to near the front the sur- 
face is quite straight, but slightly rising. It curves abruptly down- 
wards toward the ventral valve, and is much flattened on each side 
of the front margins of both valves. From side to side the curvature 
of the dorsal valve is very strong, but not regular, the valve being 
somewhat flattened along the median line, especially toward the um- 
bone. 
The median fold begins near the centre of the valve, and increases 
only slightly in prominence towards the front. Its width is about 
two-fifths that of the valve, and it is marked with four prominent, ~ 
rounded or sub-angular plications, which are separated by similar de- 
pressions. On each side of the fold there are six well defined plica- 
tions, and besides these exist one or two very indistinct ones near 
the hinge. The plications nearest the fold are the most prominent, 
being slightly smaller than those of the fold; they are rounded on top 
or slightly angular, and each slopes down more gradually on its outer 
than on its inner side. The depressions separating the plications are 
from two to three times the width of the latter. The plications are 
only faintly indicated on the umbonal region; they cause the anterior 
margins of both valves to be strongly digitate. The median septum 
of the ventral valve reaches about half way to the front; it is promi- 
nent and heavy near the beak, but grows gradually more slender for- 
ward, being reduced to a mere line near the centre of the valve. 
