Cast of the interior of the Shell of Ammonites obtusus from Lyme. Fragments of the shell remain near b. and e.

One object of this Plate and of many of the figures at Pl. 37. is to shew the manner in which the external shell is fortified by Ribs and Flutings, (PP. 340. 341.) and further supported by the edges of the internal transverse plates, that form the air chambers. See V. I. p. 348, Note. (Original.)