PTEROPODA. 215 



approaching the aperture, where the change, once induced, continues to the 

 margin. 



All the known specimens of this species occur in thinly laminated shale, and 

 are extremely flattened ; the surface-markings are frequently complicated by 

 the shell of two sides being pressed one upon the other, producing thereby 

 the appearance of intermediate, and not unfrequently the aspect of inter- 

 locking striae. This interlocking is not usually coincident with the axis, and, 

 therefore, readily distinguishable from the specific character of the preceding 

 species. 



In its general features this species presents a stronger and broader pyramid 

 than the C. continens; the angles are less rounded and the furrow sharper. 

 The transverse striae and tubercles are stronger, and the longitudinal striae 

 more continuous across the interspace. The crowding together of the transverse 

 stria) towards the aperture is not a distinguishing feature of C. continens as in 

 this species. 



In many respects this species resembles the C. Cayuga; but the transverse 

 stria; in the upper part of the shell are less distant than in that species, and 

 the interstriate ornamentation in the specimens examined is different. The 

 transverse striae are stronger than in C. undulata, and much stronger than in 

 C. crebristriala. 



Formation and locality. In the shales of the Portage group near Ithaca, N. Y. 

 It has not been satisfactorily determined in any other locality. 



CONULARIA CONTINENS var. RUDIS. 

 PLATE XXXIV A, FIGS. 7, 8. 



A single specimen in a coarse, arenaceous matrix, preserves the pyramidal 

 form, with a slight distortion from pressure. The faces are perceptibly concave 

 in the middle, becoming convex and prominently rounded on approaching the 

 margin, and are somewhat abruptly curved into the longitudinal furrow, in the 

 bottom of which the transverse stria? are regularly alternating. Along the 

 median line of each face the striae are very irregular, sometimes slightly and 



