AMMONITES. 23 



tubercles on each side of the whorl; the margin of the umbihcus is rounded off; and tiie 

 width of the aperture varies from seven to eight tenths of its height. This is the com- 

 monest form of the species. 



2d Var. costata, PI. VIII, fig. 9, of the same form and proportions as the preceding, 

 but with mere undulations of the surface in place of ribs ; the tubercles round the edges 

 of the umbilicus and of the back small, but distinct ; the other tubercles obsolete. This 

 variety is rare. • 



3d Var. intermedia of Mantell, PI. VIII, fig. 7; a much flatter shell than the 1st and 

 2d varieties, the width of the aperture being only half the height of the whorl ; the ribs 

 are prominent and more numerous, twenty in number at the umbilicus, increasing to 

 thirty at the dorsal margin ; the dorsal tubercles are distinct, the others inconspicuous. 

 Not very abundant. 



4th Var. mb-plana of Mantell, PI. VIII, fig. 10 ; proportions the same as the last, ribs 

 more numerous, but very slight ; dorsal tubercles about fifty, small but distinct ; no 

 tubercles on the side of the whorl ; umbihcus small, well-defined, with the side steep, and 

 bounded by an angular edge with very faint tubercles. Abundant at Ventnor in the Isle 

 of Wight. 



The first three varieties usually reach a diameter of two inches to two inches and a 

 half; the fourth variety rarely attains an inch and a half in diameter. 



Ammonites varians is found abundantly in the Grey Chalk, the Chloritic Marl, the 

 Chalk with siliceous grains, and the Upper Green Sand, wherever those Formations occur 

 in the southern parts of England. It is common in France in beds of the same age. 



The A. varimis of Sowerby included A. Coupei, which is here separated from it, in 

 accordance with the views of Brongniart and many other authors. The reasons for this 

 separation will be found under A. Coupei. 



The variations in form of the shells still remaining under A, varians are so con- 

 siderable, as almost to justify our regarding the 1st and 2d varieties as one species, the 8d 

 and 4th as another; or, if we admitted M. D'Orbigny's opinion, that the broader shells 

 were females and the flatter ones males, we might take the first two varieties to be the 

 former, and the last two the males -. but our present imperfect knowledge of the sexes of 

 living Cephalopods does not justify such a division. 



5. Ammonites Coupei, Brong. Plate VIII, figs. 1 — 4. Plate IX, fig. 1. 



Ammonites Coupei, Brongniart. Envir. de Paris, t. vi, fig. 3. 



— — Haan. Amm. et Gonial., No. 42. 



— — Bronn. Letbsea Geogn., t. xxxiii, fig. 4. 



— VARIANS, Sow. Min. Concb., t. 176, middle and upper figures. 



— — var. TUBERCULATA, Manteli. Foss. S. Downs, p. 116. 



— — Haan. Amm. et Goniat., No. 45. 



— — D'Orhujny. Paleont. Fran9. Terr. Cret., t. xcii, tigs. 1, 2, aud 6. 



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