Ammonites. 



MOLLUSCA. 



27 



ftat, crossed by many broad, flat, waved ribs ; wliicli, after 

 passing the centre, sweep elegantly forward ; ambit thin ; 

 aperture somewhat sagittate. 



Found in the upper Shale at Boulby, Yorkshire. 



159. A. RosTRATUs ^ The Bealted Ammonite, pi. XIX. 



fig. 10. 



Ammonites rostratus. Sowerby, Min. Conch. II. p. 163, pi. 

 172 ; Fleming, Brit. An. p. 245 ; De la Beche, Geo. Manuel, 

 p. 294. 



Compressed, carinated, with about four wholly exposed, 

 flattened volutions ; their sides crossed by large, strong, 

 remote, sligiitly bent ribs, each of which is provided with 

 tliree or four oblong tubercles ; larger on the extremity of 

 tiie ribs next the ambit, over wliich they project ; aperture, 

 elliptical, somewhat less than one-tliird the diameter of the 

 disk, and, at the ambit, terminating in a slightly reflected and 

 compressed beak, which is almost closed. The tubercles are 

 somewhat confluent on the outer volutions, but are more dis- 

 tinctly divided, and developed on the inner volutions. Great- 

 est diameter seven inches and a quarter. 



Found in Chalk Marie, Rock's Village, near Benson, 

 Oxfordshire, and in the Sussex Chalk. 



160. A. Henleyii. — Henley's Ammonite, pi. XIX. 

 fig. 11. 



Ammonites Henleyii. Sowerby, Min. Conch. II. p. 161, pi. 

 172. ; Fleming's Brit. An. p. 245 ; De la Beche, Geo. Manuel, 

 p. 371. 



Discoidal, with three or four wholly exposed, rapidly 

 increasing volutions ; sides crossed Ijy many flattened ribs, 

 which emanate from the inner sides of the volutions, curving 

 slightly from the aperture, and after reaching the centre one, 

 provided with large compressed tubercles, from whence they 

 become bifurcate, the branches gently cin-ving backwards, 

 and, after passing over the ambit, unite on the opposite side, 

 producing a crenulated margin to tlie back, when viewed 

 in profile ; the ribs are also furnislied with a tubercle, a little 

 way from their origin ; between this and the central row, the 

 volutions are a little concave ; aperture nearly orbicular, 

 being two-fifths the diameter of the disk, with a small sinus, 

 produced by the preceding volution ; greatest diameter six 

 inches. 



Found in the Lias at Lj'me Regis, Dorsetshire ; and also 

 that of Yorkshire, and the middle and south of England. 



161. A. BALTIATU3. — The Belted Ammonite, pi. XX. 

 fig. 1. 



Ammonites baltiatiis. Phillips, Geology of Yorkshire, I. 

 p. 163, pi. 12, fig. 17 ; De la Beche, Geo. Manuel, p. 372. 



Discoidal ; volutions entirely exposed ; crossed by nume- 

 rous, strong, elevated ribs, which emanate on the inner mar- 

 gins of the volutions, and pass over the rounded ambit, every 

 alternate rib being somewhat less elevated on the back. 



Found in the Lias, Yorkshire. 



162. A. DECiPiENs. — The Deceitful Ammonite, pi. XX. 

 figs. 2 and 9- 



Ammonites decipiens. Sovverbj', Min. Conch. III. 

 pi. 294, fig. 1 and 2 ; Fleming, Brit. An. p. 243 

 Beche, Geo. Manuel, p. 374. 



Discoidal, tliick ; with five or six exposed volutions, crossed 

 by large, elevated ribs, which rise a little way from the inner 

 margin, and, crossing the sides, become obscure towards the 

 ambit, which is rounded ; aperture oblong. 



This shell presents a very diS'erent ajipcarance in the adult 



p. 169, 

 De la 



and young conditions. In the latter state, when the large ribs 

 have passed the centre of the sides, they are met by nume- 

 rous small ribs, which are entirely wanting in the adult 

 shell. 



Found in Clay at Highgate Hill, and at Pakefield, near 

 Lowestoft, Suffolk. 



163. A. ovATUs. — The Ovate Ammonite, pi. XX. fig. 3. 

 Ammonites ovatiis. Piiiilips, Geology of Yorkshire, I. p. 



164, pi. 13, fig. 10 ; De la Beche, Geo". Manuel, p. 373. 



Lenticular, umbilicate ; the inner volutions entirely con- 

 cealed, their margins alone being visible within the small 

 and deep umbilicus ; sides thick internally, and sloping 

 towards the back, which is thin and slightly flattened, crossed 

 by numerous, undulating, depressed ribs, which emanate at 

 the internal margin, and after passing the centre, bend 

 sweepingly fi)r\vard. 



Found in the Hard Bands, in the Lias formation at Haw- 

 sker, Yorkshire. 



164. A. VENUSTUs The Graceful Ammonite, pi. XX. 



fig. 4. 



Ammonites venustus. Phillips, Geology of Yorkshire, I, 

 p. 122, pi. 2, fig. 48 ; De la Beche, Geo. Manuel, p. 294. 



Discoidal, thick, with three or four rapidly increasing 

 volutions, the inner ones half concealed ; sides crossed by 

 many straight, elevated ribs, equal to the interstices between 

 them ; which, on reaching the centre, are met by numerous, 

 strong, rounded, gently curved ribs, which pass over the 

 ambit, and meet with those on the opposite side, producing 

 a crenated margin at the back ; aperture oblong. 



Found in the Speeton Clay, at Speeton, Yorkshire. 



165. A. coNciNNUs The Comely Ammonite, pi. XX. 



fig. 5. 



Amynonites concinnics. Phillips, Geology of Yorkshire, 

 L p. 123. pi. 2. fig. 47. De la Beche, Geo. Manuel, 

 p. 294. 



Discoidal, thick, with four rapidly increasing volutions, 

 the inner ones half inserted ; a series of strong remote ribs 

 emanate from the inner margins of the volutions, bending 

 slightly forward, and are met in the centre by numerous, 

 acute, elevated ribs, which pass over the rounded ambit, and 

 meet with those on the opposite side ; aperture roundish. 



Found in the Speeton Clay, at Speeton, Yorkshire. 



166. A. Mjnimus The Smallest Ammonite, pi. XX. 



fig. 6. 



Ammonites, " like A. parvus." Phillips, Geology of 

 Yorkshire, I. p. 187, pi. 2, fig. 46. 



Discoidal, thick, with three volutions, the inner ones two- 

 thirds inserted, and the outer ones increasing rapidlj' ; sides 

 crossed by numerous, curved ribs which rise on the inner 

 margins, and pass over the rounded ambit, meeting those of 

 the opposite side ; aperture oblong. 



Found in the Speeton Clay, Yorkshire. 



167. A. cuRviNoiDEs. — The Curved-Ribbed Ammonite, 

 pi. XX. fig. 7. 



Ammonites curvinoides. Phillips, Geology of Yorkshire, I. 

 p. 123, pi. 2. fig. 50 ; De la Beche, Geo. Manuel, p. 294. 



Volutions, flattened with remote, elevated, waved ribs, 

 which emanate from the inner edges of the volutions, and as 

 they approach the ambit are suddenly and acutely curved 

 towards the aperture ; between these are several depressed 

 and nearly obsolete ribs ; ambit rather thin. 



Found in the Speeton Clay, Yorkshire. 



