NIAGARA GROUP. 263 
ceding, has its representative in the shaly limestone of the Helderberg, where a larger species 
presents the same characters of surface in all its details. 
Fig. 3 a, b, c. Ventral views, presenting the ordinary characters of well preserved specimens. 
Fig. 3 d. An individual, still preserving its natural proportions, where the beaks are widely se¬ 
parated, with a broad cardinal area and little extension of the cardinal extremities. 
Fig. 3 e, /, g. Profile views of three specimens, showing the variable elevation of the beak of 
the dorsal valve, and width of the area. 
Fig. 3 h, i. Front views of specimens, showing a different proportional convexity. 
Fig. 3 k. A portion of the surface enlarged. 
Position and locality. In the shale at Lockport, Lewiston, and rarely in other places. 
624. 7. SPIRIFER BICOSTATUS. 
Pl. Liv. Fig. 4 a - e. 
Orthis bicostatus # . Vanuxem, Geol. Rep. 3d Dist. N. York, 1842, pag. 91 and 94. 
Somewhat obovate-triangular, the dorsal valve gibbous, with the beak extended and incurved 
over a short triangular area ; ventral valve convex ; surface marked by conspicuous concentric 
subimbricating stride ; dorsal valve with a distinct plication on each side of the sinus, and 
towards the base are two other obscure plications on each side, presenting three and sometimes 
four gentle undulations on the margin on each side of the centre ; cardinal line shorter than 
the width of the shell, and the area scarcely extending so far as the cardinal line ; extremities 
distinctly rounded. 
This species is intermediate in its characters between S. crispus and S. ptychodes. The con¬ 
centric striae are slightly dissimilar from those of S. crispus., in appearing to imbricate more 
distinctly. The plications, except one on each side of the sinus of the dorsal valve, rarely reach 
the beak, and usually appear only near the base or on the margin. It may be readily confounded 
with S. crispus ; but the shorter hinge-line, and abrupt curving of the striae at the extremities, 
are sufficient to distinguish it from that species, even where the plications are insufficient. 
The specimen figured has the ventral valve compressed, and I have not been able to see one 
with this valve perfect, though the dorsal valve is not uncommon. 
Fig. 4 a. Dorsal valve of an individual of this species. 
Fig. 4 b. Ventral view of the same, showing the area and foramen, the beak of the ventral valve 
being broken off. 
Fig. 4 c. Profile view, showing the form of the dorsal valve. 
Fig. 4 d. Front view, in which the elevation of the ventral valve is given as it appears to have 
been in its perfect state. 
F ig. 4 e. An enlarged portion of the surface, showing the character of the strite. 
* This species was labelled by Mr. Conrad, in Mr. Vanuxem’s collection, Orthis bicostatus; but the name has 
been published, so far as I know, only in the report of Mr. Vanuxem cited above. 
