This Plate presents a longitudinal view of the same fossil, of which a side view is given in the last figure. The same transverse plates, that approximate so closely beneath the sides of the shell, where it is flat and feeble, (Pl. 38.) are distant from each other along the dorsal portion, which from its convex form is strong.

The Siphuncle is preserved in its proper dorsal place at d.

The elevations and depressions of the transverse plate in front of this figure exemplify the theory of Von Buch, respecting the use of the Lobes and Saddles formed by the undulations of its outer margin. See V. I. p. 353, and Note. (Original.)