Ammonites. 



CEPHALOPODA. 



245 



Discoidal, with six or seven volutions, two-thirds exposed, 

 smooth ; transvei-sely ribbed, altcniately two short, reachiug 

 half across the volution, and one long, emanating from the 

 dorsal margin, the longer ones becoming thickened towards 

 the inner ma)-gin; shorter ones curved backwards, near the 

 dorsal edge ; ambit or back roimded, with a slight depression 

 in the middle, formed by the ribs, which nearly meet ; aperture 

 terminating on each side with a spatulate projection of about 

 one and a half inch in length, and three-eighths iu width. 



In the Oxford Clay, Christian Malford. 



10. Ammonites Euzabethji;. — Elizabeth's Ammonite, pi. 

 XX.** figs. 1, 2, 3. 



A. ElizabetheB. Pratt, Ann. Nat. Hist. VIII. p. 1(52, pi. 3, 

 figs. 1 — 4. 



Volutions six or seven, about two-thirds exposed ; angular, 

 arising from a series of spines on each dorsal edge, and two 

 rows of tubercles on the sides of the volutions, one near the 

 middle, another smaller and compressed, near the inner mar- 

 gin; sides with transveree ribs, varying much in elevation, 

 curvatures, and number ; iu some they are nearly straight, in 

 others curved, and in another variety undulating, but generally 

 becoming angular near the aperture in the adult shell ; some 

 form loops on the surface ; aperture provided with a lengthened 

 spatulate projection, its surface deeply marked by lines of 

 growth ; back narrow, concave, the ribs passing over it ; 

 siphuncle not visible. 



The great difference in those figured certainly would lead 

 to tlie supposition that they ai-e specifically distinct. I yield, 

 however, to the opinion of Mr. Pratt, who has had an oppor- 

 tunity of examining more varieties than I have done. He 

 says, that their characters "appear to indicate several distinct 

 species, but on close examination, it is seen that all the 

 varieties pass into each other, the same specimen sometimes 

 containing more than one form." 



The spines and rays (ribs) vary from sixteen to upwards of 

 sixty on the last volution, and they are large and elongated in 

 proportion to the smallness of their number. 



The Oxford Clay, Christian Malford. 



] 1. Ammonites Sttjtchburii. — Stutchbury's Ammonites. 



A. Stutchbiirii. Pratt, Ann. Nat. Hist. VIII. p.lC3, pi. 4, f 1 , 2. 



Discoidal, with four two-thirds exposed volutions ; sides with 

 a series of short, distant, curved ribs, emanating from the inner 

 sides of the volutions, terminating in compressed tubercles ; 

 beyond these, to the outer mai-gin, are \evj numerous close-set 

 waved ribs ; back narrowed, with the smaller ribs passing over 

 it, and with a series of sharp serrated projections on both sides ; 

 aperture with a projecting beak. 



The 0.xford Clay, Christian Malford. 



12. AstMONiTEs FLUCTCOsns.— The Fluctuating Ammonites, 

 pi. XX.** fig. 16. 



A. fiuctuosus. Pratt, Ami. Nat. Hist. Vlll. p. HJl, pi. 0, 

 figs. 1. 2. 



Discoidal or lenticular, surface smooth, with six two-thirds 

 exposed volutions ; crossed by thick, distant ribs, which, with 

 a few exceptions, are forked for nearly their outer half ; back 

 plain. 



In the young condition there are numerous sharp, alternately 

 long and short, ribs, the short ones combining in twos or threes 

 with the longer ones about the middle of the sides, some 

 remaining distinct. 



The OsSord Clay, Christian Malford. 



1 3. Ammonites Sedgwickii. — Sedgwick's Ammonite. 



A. Sedgwickii. Pratt, Ann. Nat. Hist. V'lII. p. 103, pi. 5, 

 fig. 1. 



Discoidal, smooth, with five one-fourth exposed volutions, 

 with a row of distant tubercles on the inner side, situated a 

 little way from the margin ; outer sides with numerous flat, 

 close-set ribs, which do not reach half way across the volutions. 



The Oxford Clay, Christian Malford. 



14. Ammonites Brightii. — Bright 's Ammonite, pi. XX.** 

 figs. 4 and 10. 



A. Brightii. Pratt, Ann. Nat. Hist. VIII. p. 164, pi. 6, 

 figs. 3, 4. 



Discoidal, nearly smooth, with about seven two-thirds exposed 

 volutions ; with sevei-al flat, obtuse ribs emanating from the 

 dorsal edge, which combine a little beyond the middle of the 

 volutions into compressed, elongated tubercles, which reach 

 the inner margin; the tubercles being about one-third as 

 numerous as the ribs, and meet them in a rounded right angle ; 

 the siphuncle is distinguished by a sharp ridge on the back. 



The Oxford Clay, Christian Malford. 



15. AmmonitesLonsdalii. — Lonsdal's Ammonite, pi. XX.** 

 fig. 15. 



A. Lomdalii. Pratt, Ann. Nat. Hist. VIII. p. 164, pi. 5, f. 2. 



Discoidal, three or four one-third exposed volutions, the last 

 being more than half the diameter of the shell : surface wth 

 numerous transverse waved ribs, which emanate from the back, 

 and hardly reach the middle of the volutions, become fewer and 

 more obtuse as the shell increases iu size, and pass into fine 

 striae near the aperture, whicii forms a regular concave termi- 

 nation, except on the inner edge, where it bends back, some- 

 what like the handle of a sickle. 



The O.vford Clay, Christian Malford. 



10. Ammonites solcatcs.— The Furrowed Ammonites, jil. 

 XX.** figs. 5, 0,11.12. 



A. sulcatus. Strickland, Geo. Chelt. p. 105, pi. II, figs. 1, 

 2,3. 



Moderately convex, with three or four volutions, almost 

 wholly exposed ; crossed by alternately long and short curved 

 strong ribs, increasing in thickness from the inner to the outer 

 side ; back with a deep furrow in the young state, which 

 becomes obliterated when old ; when young, the ribs are fine 

 and close : back square in the adult ; aperture oblong. 



The Lias Shales, Vale of Gloucester. 



