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 Maecurii, 

 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, w^here 

 the fold and sinus reach the margin. 



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 generally 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 

 cruras 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 



