44 



Spirifera Gaspensis. (N. sp.) 



Plate 3, figs. 8, 8a, 8b, 

 Spirifera Gaspensis, Geol. Can., p. 398. 



D escript on. — Shell varying from semi-circular to transversely semi- 

 elliptical, hinge-line much extended ; often twice the length of the shell ; 

 in some specimens shorter, one-fourth or only one-fifth greater than the 

 length. In the wide specimens the cardinal angles are acute, varying 

 from 40° to 90'^, sometimes a small portion of the sides, usually about one 

 line in length, at right angles to the hinge ; the remainder of the sideSy 

 around to the mesial fold or sinus, uniformly and gently rounded. In 

 those with a short hinge, the sides, in the upper half of the shell, are 

 straight or slightly concave, and at about 90^ with the hinge line, the 

 front half rounded. Ventral valve strongly convex, most elevated about 

 the middle of the upper half, or a little above that point ; cardinal angles 

 more or less flattened ; umbo prominent ; beak small, strongly incurved ; a 

 well-defined mesial depression, concave or sub-angular in the bottom without 

 ribs, extends from the beak to the front margin where it strongly elevates 

 the edge of the dorsal valve, and, extending the whole width, slightlj 

 concave, one or two lines high at the beak. Foramen about three lines- 

 wide in a specimen of average size ; deltidium convex, apparently not 

 entirely closing the foramen. Dorsal valve with a strongly elevated mesial 

 fold, without ribs ; on each side of the fold moderately convex, compressed 

 near the cardinal angles ; umbo and beak curved down to the area, which 

 is small, and apparently nearly in the plane of the margin, but sloping a 

 little outwards. On a side view, the outline of this valve rises, with a 

 more or less abruptly rounded curve, to about one-third the length of the 

 valve and then becomes nearly parallel to the lateral margin, and continues 

 to the front with a gently convex curve. The front margin, owing to 

 the great elevation of the mesial fold, is nearly squarely truncated, as seen 

 in the side view- 



Surface with from twelve to eighteen simple undivided ribs, on each 

 side of the fold and sinus. These are often crossed by concentric zig-zag 

 imbricating lines of growth. In the casts, the ribs vary from acutely 

 angular to rounded angular. When the shell is preserved the ribs are 

 obtusely angular. 



In the casts of the interior (the condition in which the specimens are 

 usually found in the sandstone) the mesial fold of the dorsal valve often 

 exhibits a fine groove along the middle, as if impressed by a thin septum. 

 This is not visible in all the specimens, especially those that are slightly 



