Ammonites. 



MOLLUSCA. 



13 



each other at their margins. Greatest diameter varying from 

 twelve to eighteen and even twenty inches. 



Found in the Lias, in the middle and south of England, 

 and also in the Lias at Lyme Regis. 



In the larger specimens there is no appearance of ribs, but 

 sometimes with a few very remote, slightly indented, diver- 

 gent furrows, such as we have represented. This beautiful 

 species is frequently formed of pyrites, and exhibits on its 

 surface the most splendid iridescent play of colours. 



This species was named by Sowerby in honour of the cele- 

 brated and munificent geologist, J. B. Greenougli, Esq. of 

 London. 



51. A. VERTEBRALis. — The Jointed Ammonite, pi. IX. 

 fig. 9. 



Ammotnles vertehralis, Sowerbj^ Min. Conch. II. p. 147, 

 pi. 165, tigs. 1, 2. 



Discoidal, carinated, five volutions, the inner ones partly 

 inserted ; sides furnished witli numerous prominent, sliglitl3' 

 undulating ribs, which are tuljerculate in tiie centre, from 

 whence they are regularly bifurcate, each branch being pro- 

 vided with a somewhat acute, compressed tubercle near its 

 middle, from whence the branches curve towards the keel, 

 where, at their termination, another slightly reflected tubercle 

 is produced, and the branches reunite on the opposite side ; 

 keel serrato-tuberculafe, resembling in some measure the 

 vertebral column in mammalia; aperture ten-sided. 



Found in the beds of Siliceous sand at Dry Sandford and 

 Marsham, near Abingdon, Berkshire. 



52. A. coNCAVus.— The Concave Ammonite, pi. IX. fig. 11. 

 Ammonites concavus, Sowerby, Min. Conch. I. p. 214, pi. 



94, lower figure. 



Discoidal, involute, compressed, carinated, umbilicate ; with 

 four exposed volutions, concave near the centre, crossed by 

 numerous, curved, unequally long ribs, which are less distinct 

 towards their centre ; keel sharp, entire ; aperture half the 

 diameter of the disk, acutelj' triangular ; external angle sub- 

 rotund, with the interior angles obliquely truncated. 



Found at Ilminster. 



53. A. Bechei. — De La Beche's Ammonite, pi. IX. fig. 12. 

 Ammoni/es Bechei, Sowerby, Min. Conch. III. p. 143, pi. 



280, figs. 1, 2. 



Gibbous, umbilicate ; inner volutions entirely concealed ; 

 sides very prominent, with numerous nearly straight trans- 

 verse ribs, about two to each tubercle, which are less deve- 

 loped towards the centre, but increase in strength as they 

 approach the much rounded ambit, over which they pass con- 

 tinuously ; these are crossed by many close, elevated, con- 

 centric stri.e ; each side provided with two rows of numerous, 

 small, slightly depressed tubercles, those of the inner row 

 most prominent ; between these rows the sides are a little 

 flattened ; aperture large, as wide as it is long, occupying 

 half the diameter of the shell. 



Found in the Blue Lias at Lyme Regis, Dorsetshire. 



54. A. Ei.GGANs. — The Elegant Ammonite, pi. IX. fig. 13. 

 Ammonites elegans, Sowerby, Min. Conch. I. p. 213, pi. 94, 



upper figure. 



Discoidal, involute, with a very acute entire keel, within 

 which the small siphuncle is placed ; three to four volutions, 

 much compressed on the sides, the inner ones about two- 

 thirds inserted ; furnished with numerous, equal, doubly 

 curved ribs ; aperture acutely triangular, occupying about 

 two-thirds of the disk ; internal angles truncate ; thickness of 



the shell about one-third its diameter ; septa rather close, 

 witli their margins sinuous and greatly plaited. 



Discovered between Ilminster and Yeovil by Mr Strange- 

 ways. 



55. A. PLANULATUS. — The Flattened Ammonite, pi. X. 

 fig. 1. 



Ammonites planulattis. Sowerby, Min. Conch. VI. p. 136, 

 pi. 570, fig. 5. 



Discoidal, compressed ; volutions four, inner ones about 

 one-third inserted, and fiat as far as is exposed, flattened on 

 the sides, and contracted by four or five varices, the whole 

 with their inner half plain, the other having numerous, broad, 

 slightly bent, regular, equidistant ribs, passing over the back, 

 which is much rounded ; aperture oblong-oval. 



Found by G. Mantell, Esq. in a Marie pit at Hamsey, near 

 Lewes. 



56. A. SuTHERLANDi^ Sutherland's Ammonite, pi. X. 



fig. 2. 



Ammonites SutherlandicB. Marchison, Geological Trans- 

 actions, 2d Series, II. pt. 2, p. 323 ; Sowerby, Min. Conch. 

 VI. p. 121, pi. 563, figs. 1, 2. 



Discoidal, gibbous, umbilicate ; two or three volutions, 

 inner ones much inserted ; and onlj- partly seen within the 

 large and deep umbilicus ; sides smooth and plain ; back very 

 thick, and regularly rounded ; length of the aperture about 

 equal to half the diameter of the shell, which is nearly ten 

 inches. 



Discovered by R. I. Murchison, Esq. in the White sand- 

 stone at Braambur}' Hill, Brora, Sutherlandshire, and in the 

 Coral Oolite and Calcareous grit of Yorkshire. 



Named in honour of the Duchess Countess of Sutherland. 



There is a remarkable specimen in the Collection of the 

 Geological Society, which was found by the quarrymen, and 

 presented to the late Duke of Sutherland. It was supposed 

 to have been a fossil human skull ; it is compressed, and 

 somewhat resembles a Scaphite. 



57. A. SELLiGuiNous The Selliguinous Ammonite, pi. X. 



fig. 3. 



Amiiionifes l<cvigatus. Sowerby, Min. Conch. VII. p. 93, 

 pi. 540, fig. 1. 



Discoidal, smooth ; inner volutions few-, almost wholly 

 inserted, the outer one enlarging rapidly ; external margin or 

 ambit obtuse ; aperture very narrow, forming an elongated 

 ellipsis, which is rendered sagittate by the indentation of the 

 volution. 



Discovered in the Folkstone Marie, near Warminster, by 

 Miss Bennet, and found at Cheriton, near Sandgate, Kent, in 

 the Tile clay, by Dr Fittom. 



58. A. ciNCTUs. — The Girdled Ammonite, pi. X. fig. 4. 

 Ammonites cinctus. Mantell, Geology of Sussex, p. 116; 



Sowerby, Min. Conch. VI. p. 122, pi. 564, fig. 1. 



Discoidal, subumbilicate ; volutions three, depressed, three- 

 fourths inserted, with transverse, annular, bifurcate, undulated 

 ribs ; umbilicus expanded, with a marginal zone of oblique 

 tubercles ; ambit convex, embraced by the ribs ; aperture 

 ovato-sagittate. 



Mantell says of his specimen, " The volutions, although 

 compressed, have a slight degree of convexity, and are orna- 

 mented by transverse radiations that arise from a row of small 

 tubercles on the inner margin. Each radius (rib) divides into 

 two branches, which pass with a gentle sweep across the 

 ambit, and unite with the corresponding undulations of the 



