EXPLANATION OF THE PLATES AND WOOD-CUTS. 



whorl. Diameter 7 inches, width of the aperture li inch, its length 2^ inches. 

 A larger specimen measures 9i inches across, and is less plaited and ribbed. The 

 figure is drawn ird of the natural size. 



Very near A. decipiens (M. C.),but the whorls increase more rapidly and envelope 

 each other more. 



Fig. 10. Ammonites Pottingerii. Discoid, thick, costated ; inner whorls exposed ; 

 front nearly flat ; ribs sharp, prominent, split into two or three over the front ; 

 aperture transversely obovate. Diameter 4^ inches, width of the aperture 1 inch 

 8 lines, its length 1 inch 2 hues. 



A very distinct species, cast in coarse limestone, replete with large grains of quartz. 



Fig. 1 1. Ammonites fissus. Discoid, costated ; whorls rapidly increasing, the inner 

 exposed. Costse large, obtuse, either forked or simple, with an intermediate short 

 rib passing over the front, which is convex and prominent ; aperture ovate. Dia- 

 meter 4^ inches, width of the aperture 1 inch 5 lines, its length 1^ inch ; the 

 figure is reduced to one half. 



Fig. 12. Ammonites torquatus. Discoid, costated ; inner whorls exposed ; costae nu- 

 merous, generally split into two as they pass over the rounded front, sometimes 

 single, and (in large specimens) occasionally trifid ; inner edges of the whorls in- 

 curved ; aperture orbicular ; whorls about five. Diameter 2f inches, width of 

 aperture 1 inch, its length the same. 



In large specimens are indications of a thickened edge having been formed 

 to the aperture at various periods of growth. It is like A. annulatus vulgaris 

 (Zieten, PI. IX. f. 1.), and also A. colubrinus major {Id. PI. IX. f. 3.), but distin- 

 guished by the incurved inner margin from both, as well as from a similar species 

 found in the Himalaya Mountains. 



Fig. 13. Ammonites Fornix. Discoid, compressed, (when young, keeled,) undulated; 

 inner whorls ^rd exposed, their exposed parts smooth ; margin convex, smooth, 

 with a row of minute tubercles on each side, and a slender keel, which are lost in 

 the external whorls ; undulations bent back in the middle of the sides, divided to- 

 wards the margin ; aperture sagittate, elliptical. Diameter 2 inches, width of 

 aperture 7 lines, its length 1 inch 2 lines. 



Fig. 14 a. to/. Nummularia exponents. Very flat, thin, granulated, whorls few ; septa 

 rather distant, visible through the shell ; chambers twice as long as deep. Diameter 

 of the shell frequently more than an inch. Fig. 14/. is a magnified section. 

 When young, this Nummulite is lenticular ; when old, it is concave in the centre, 



