Rathbun.] 26 [May 15, 
denaria, and in this character alone does it appear to differ from S. 
speciosa Schloth., of England and Germany. There exists in the col- 
lection of the Geological Commission a fragment of a ventral valve 
of very large size, five or six times that ordinarily attained by this 
species. 
Very abundant in the Devonian sandstone of the Rio Mecurt, 
but not found at either of the two other Devonian localities. (Geol. 
-Comm., 1876.) 
Spirifera Derbyii, sp. nov. 
Shell of medium size, transverse; broadly semi-elliptical in outline ; 
proportions of length to breadth about as 3 to 4; hinge line slightly 
shorter than the width of the shell; cardinal angles regularly rounded. 
The lateral margins, together with the anterior, form quite a reg- 
ular, broad, semi-elliptical curve, slightly indented in front, where 
the fold and sinus reach the margin. 
4 
Dorsal valve moderately gibbous, and most elevated just posterior 
to the middle, towards which the surface arches up rapidly from the 
beak, but it curves down more gradually toward the front, the sur- 
face being slightly flattened on the fold, anterior to the middle. 
From the median fold the sides slope quite regularly to the lateral 
margins, and are nearly straight. Beak small and only slightly pro- 
duced beyond the hinge line; median fold prominent, much elevated, 
and increasing quite rapidly in size toward:the front. At the beak it 
is very fine, and rounded on top, but toward the front it becomes 
flattened. Throughout its entire length it is quite narrow above; its 
sides are broad and straight and slope abruptly downwards. Propor- 
tions of the width of the fold on top to its width below, at the front 
margin, about as 1 to 3. There are on each side of the fold five regu- 
larly rounded, simple plications, and gvenerally a sixth indistinct one 
can be made out. These plications are very much smaller than the 
fold, and they are separated by rounded depressions of equal or 
slightly greater width. The first three plications on either side are 
well defined and begin quite close to the beak; the fourth, fifth and 
sixth are successively smaller and more flattened. The bases of the 
crure on each side of the beak are quite broad and heavy. 
All the specimens definitely referable to this species are dorsal 
valves; there was found, however, a fragment of the ventral valve 
of a Spirifera, which may belong to this species. It has a moder- 
ately deep, rounded sinus, and six rounded plications on each side. 
The hinge area is of moderate width and curved; the beak, small 
