Ammonites. 



MOLLUSCA. 



17 



volutions, with numerous, somewhat obtuse, slightly curved 

 ribs, emanating from the suture, and passing over the back, 

 where the}' become more elevated, and each rib is furnished 

 with two small short spines on both sides, situate near the 

 inner and outer edges of the volutions ; aperture obovate. 



Discovered in the Lias at Pabba, Western Islands of Scot- 

 land, by R. J. Murchison, E:^q. ; and also in the Lias of 

 Yorkshire. 



82. A. pi.ANoRBis The Planorbis-shaped Ammonite, 



pi. Xn. fig. 7. Fleming, Brit. An. p. 248. 



Ammoniies planorbis. Sowerby, Min. Conch. V. p. 69. pi. 

 448. Fleming, Brit. An. p. 248. 



Discoidal, with three or four smooth, rapidly increasing 

 volutions, two-thirds exposed, much compressed, and crossed 

 by numerous very fine lines of growth. 



This Ammonite, for the most part, exhibits, on its external 

 surface, the most beautiful iridescent reflections. 



Found in the slaty clay, connected witli the Lias, at Wat- 

 chet, Somersetshire, and also in Lincolnshire. It is by no 

 means scarce. 



83. A. GuLiEi-Mii. — Williams's Ammonite, pi. XII. fig. 8. 

 Fleming, Brit. An. p. 246. 



Ammonites Gidielmii. Sowerby, Min. Conch. IV. p. 5. 

 pi. 311. 



Lenticular, much compressed, with a narrow and flat ambit; 

 five or six exposed volutions, crossed by numerous dissimilar, 

 arcuated, acute ribs ; each of the longer ones provided with a 

 tubercle at their inner ends, and another at about a third of 

 their length. Here they divide and alternate with shorter 

 and more numerous ribs, which terminate in a border of 

 round, prominent, distinct tubercles, on each side of the 

 ambit ; aperture elliptical, somewhat more than one-third as 

 wide as long. 



Found in the Oxford claJ^ south-west of England. 



It is named to commemorate Dr George Williams, Professor 

 of Botany, Oxford. 



84. A. Blagdeni Blagden's Ammonite, pi. XII. fig. 9. 



Fleming, Brit. An. p. 245. 



Ammonites Blagdeni. Sowerby, Min. Conch. II. p. 2-31. 

 pi. 201. Phillip's Geology of Yorkshire, I. p. lol.; De la 

 Beche, Geo. Manuel, p. 371- 



Sub-cylindrical, very deeply umbilicate, occupying the 

 entire disk ; five or six volutions, almost wholly exposed, 

 crossed by numerous strong radiating ribs, which gradually 

 thicken as they diverge from the centre, each terminating 

 upon the outer edge, by a large spiniform tubercle. The 

 inner volutions are deeply sunk, and not above an eighth of 

 the thickness of the ambit, which is very broad, slightly con- 

 vex, and fluted, to the extent of four or five furrows to each 

 of the marginal tubercles ; aperture transverse, quadrangular, 

 and three times as wide as long ; greatest diameter, about six 

 inches and three quarters ; thickness, four and a half inches. 



Found in the Great or Bath Oolite of Yorkshire, and in 

 the Inferior Oolite at Dundry and also in Normandy. 



Named in memory of Sir Thomas Blagden. 



85. A. Leachii. — Leach's Ammonite, pi. Xll. fig. 10. 

 Ammonites Leachii. Sowerby, Min. Conch. III. p. 73, pi. 



242, fig. 4. Fleming, Brit. An. p. 243. 



Compressed, with four volutions ; the inner ones half 

 inserted ; crossed by numerous, undulating, prettj' prominent, 

 frequently furcated ribs, which are arcuated as thej' pass 

 over the front, inclining to the aperture ; ambit sharp, 

 crenated ; aperture ovate. 



Found in the Lias at Weymouth ; and named in honour of 

 Dr William Elford Leach, the late distinguished zoologist 

 of the British Museum. 



This species is nearly allied to Ammonites Lamberti. pi. 



V. fig. 1 ; but differs from it in being more gibbous, and in 

 the ribs being more prominent and less numerous. 



86. A. coRRUGATUS The Wrinkled Ammonite, pi. 12, 



fig. 11. Fleming, Brit. An. p. 244. 



Ammonites coirugatus. Sowerby, Min. Conch. V. p. 74, 

 pi. 451. fig. 3 ; Ue la Beche, Geo. Manual, p. 375. 



Discoidal, carinated ; having four volutions, crossed by 

 numerous, elevated, slightly carved, and furcated ribs, the 

 furcations near the centre ; the minor ones three-fourths con- 

 cealed ; with a broad umbilicus, which exposes part of the 

 inner volutions ; back obtuse, with a distinct carina in its 

 centre ; aperture obovate. 



Found at Dundry, in the Iron-shot Oolite. 



This shell somewhat resemljles the Ammonites IcBviuscuhis, 

 pi. X VH. fig. 7, but is considerably thicker, the back broader, 

 and the ribs more prominent. 



87. A. FUNiFERUs. — The Corded Ammonite, pi. XIIL 

 fig. 1. 



Ammo7iites funifertis. Phillips, Geologj' of Yorkshire, I. 

 p. 142, pi. 6. fig. 23. 



Lenticular, deeplj' umbilicate, carinated, thick in the 

 centre, and thin at the external margins ; slightly and 

 obscurely ribbed transversely, with stronger grooves passing 

 over the thinly carinated back ; inner volutions concealed ; 

 apertiu-e acutely sagittate, much compressed, and nearly 

 equal in length to half the diameter of the shell ; greatest 

 diameter about four inches. 



Found in the Kelloways Rock at Scarborough. 



This species is nearly allied to Ammonites excavatus, pi. 



VI. fig. 7. 



88. A. PTYCHOMPHALus. — The Plaited-umbilicus Ammo- 

 nite, pi. XIII. figs. 2 and 11. 



Ammonites plicomphalus. Sowerby, Min. Conch. IV. 

 p. 82 and 145, pi. 359 and 404. Fleming, Brit. An. p. 244. 

 De la Beche, Geo. .Man. p. 370. 



Discoidal, largelj' umbilicate, around which are from eight 

 to ten divergent, wide, somewhat acute protuberances ; 

 ambit rounded and plain ; aperture ovate, about three- 

 sevenths of the last volution in size ; a little straitened 

 towards the back ; greatest diameter about five inches and a half 



Figure 2 represents the adult fossil, and figure 11 the 

 young, in which condition it is very different firora the old 

 state, being provided with numerous, close, slightly bent, 

 transverse furrows. 



Found in the sandstone at Bolingbroke, Lincolnshire, by 

 Mr Weir ; the Kimmeridge clay, Yorkshire ; and in the 

 Oxford clay, Normandy. 



89. A. LENTicuLARis. — The Leus-shaped Ammonite, pi. 

 XIII. fig. 3. 



Ammotiites /enticularis, Phillips, Geology of Yorkshire, I. 

 p. 142, pi. 6, fig. 25. 



Lenticular, smooth, inner volutions concealed, umbilicate, 

 with a plain, slightly rounded keel ; aperture sagittate, 

 equal to nearly the half of the diameter of the shell ; consi- 

 derably thickened in the centre, and sloping off towards the 

 thin smoothly carinated ambit. 



Found by Pi'ofessor Phillips, in the Kelloways Rock at 

 Scarborough. 



