24 



MOLLUSCA. 



Ammonites. 



within the circumference of the small, shallow umbilicus ; 

 outer volution very large, its sides rather convex, ornamented 

 with slightly elevated, smooth, waved, alternately long and 

 short ribs, or undulations ; ambit obtuse, the carina large and 

 prominent ; aperture sagittate, occupying a half of the dia- 

 meter of the disk ; tiie size of the umbilicus being a third of 

 the remaining half. 



In young shells, the inner volutions are exposed, the 

 umbilicus larger, the ribs more conspicuous, and the aperture 

 square and oblong, less in proportion to the size of the disk ; 

 as the shell enlarges, it becomes longer, more deeply indented 

 by the preceding volution, and more narrowed towards the 

 front. 



Discovered in the Inferior Oolite at Dundry, by G. W. 

 Braikenridge, Esq. and occurs in the same strata, Normandy. 



132. A s,TRiATULUs. — The Minutely-Striated Ammonite, 

 pi. XVII. fig. 8. 



Ammonites strialidus. Sowerby, Min. Conch. V. p. 23, 

 pi. 4:21, fig. 1. Fleming, Brit. An. p. 244. De la Beche, 

 Geo. Manuel, p. 37 !• 



Discoidal, carinated; with six convex, entirely exposed 

 volutions ; sides with numerous slender, doubly undulated 

 ribs ; the whole surface covered with minute striae, which lie 

 parallel to the ribs ; carina but slightly produced ; aperture 

 elliptical, its length being about a fourth the diameter of the 

 disk. 



Discovered in a Marly Limestone nodule, in Robin Hood's 

 Bay, Yorkshire, by Mr Crawford of Scarborough ; and occurs 

 not unfrequenlly in the Inferior Oolite and Lias of Yorkshire. 



133. A. Banksii. — Banks's Ammonite, pi. XVII. fig. 9- 

 Ammonites Banksii. Sowerby, Min. Conch. II. p. 229, 



pi. '200. Fleming, Brit. An. p. 245. De la Beche, Geo. 

 Manuel, p. 373. 



Discoidal ; umbilicate very thick, with five or six rounded 

 volutions, with their margins well relieved ; sides concave, 

 provided with a row of ten or eleven large, round, obtuse 

 tubercles ; back slightly convex, and with a series of oblique 

 fluted grooves, towards the aperture ; inner volutions nariow, 

 the outer one very thick, and equal to the remainder of the 

 disk ; aperture transverse, its length thrice its width. 



Found in the Inferior Oolite, Dundry. 



Named in honour of the late distinguished friend of science. 

 Sir Joseph Banks. 



134. A. RusTicus. — The Rude Ammonite, pi. XVII. fig. 10. 

 Ammonites rusticus. Sowerby, Min. Conch. II. p. 171, ph 



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

 p. 293. Mantell, Geology of Sussex, p. 199. 



Depressed ; with about three gibbous exposed volutions, 

 each provided on both sides with a row of conical obtuse 

 tubercles, and two rows of slightly elevated ones around 

 the broad and flattened ambit, the bases of the larger ones 

 spreading widely, and nearly connected ; aperture ^ wider 

 than long, its inner side concave, and considerably shorter 

 than the other angles. 



This is a ponderous clumsy species, and is of frequent 

 occurrence in the Lower Chalk at Southerham, but the speci- 

 mens are very imperfect. Sowerby says it occurs at Comb 

 Payne, near Lyme Regis, Dorsetshire. It is also met with 

 in the Lower Chalk of Lewes, according to Mantell. 



This Ammonite has some affinity to A. catinus, pi. XIII. 

 fig. 4, but is distinguished bj' the two dorsal rows of tubercles, 

 and the "ibbous form of the volutions. 



135. A. MARGiNATUs. — The Bordered Ammonite, pi. 

 XVin. fig. 1. 



Ammonites marginatus. Phillips, Geo. Yorkshire, I. p. 

 123, pi. 2, fig. 41 and 43. De la Beche, Geo. Manuel, p. 294. 



Subglobose ; umbilicate ; carinate ; the edges of the inner 

 volutions only visible in the large deep and conical umbilicus ; 

 which has a subcarinated margin, and a series of round, pro- 

 minent tubercles along its edge ; outer volution very large, 

 thick, and slightly wrinkled transversely ; carina prominent 

 and sharp. 



The young shell is destitute of tubercles on the margin of 

 the umbilicus. 



Found in the Speeton Clay, Yorkshire. 



136. A. MACULATUS. — The Spotted Ammonite, pi. XVIII. 

 fig. 2. 



Ammonites maculatus. Phillips, Geology of Yorkshire, I. 

 p. 163, pi. 13, fig. 11. De la Beche, Geo. Manuel, p. 371. 



Discoidal thick ; with five or six exposed volutions, with 

 flattened sides, crossed by numerous, straight, elevated ribs, 

 which emanate from the inner margins, and pass over the 

 broad, flat ambit, proceeding continuously to the inner 

 margins of the volutions on the opposite side ; aperture nearly 

 orbicular. 



Found in the Lias of Yorkshire. 



137. A. siGMiFER The S. Ribbed Ammonite, pi. XVIII. 



fig. 3. 



Ammonites sigmifer. Phillips, Geology of Yorkshire, I. p. 

 164, pi. 13, fig. 4. De la Beche, Geo. Manuel, p. 372. 



Discoidal, carinated ; with four somewhat compressed 

 volutions, crossed by rather distant curved ribs, which 

 emanate from the inner edges of the volutions, and after 

 passing the centre, bend elegantly forward ; inner volutions 

 half concealed and increasing rapidly ; carina sharp and broad 

 for the size of the shell. _ 



Found in Calcareous nodules, in the Lias formation of 

 Yorkshire. 



138. A. DISCUS. — The Quoit Ammonite, pi. XVIII. fig. 4. 

 Ammonites discus. Sowerby, Min. Conch. I. p. 37, pi. 12. 



De la Beche, Geo. Manuel, p. 373. 



(See description, page 12, No. 48.) 



Found in the Inferior Oolite, Dundry, Yorkshire ; and in 

 the Cornbrash, middle and south of England. 



139. A. coMPRESiUs. — The Compressed Ammonite, pi. 

 XVIII. fig. 5. 



EUipsolites compressus. Soweiby, Min. Conch. I p. 81, 

 pi. 38. 



Elliptical, compressed, smooth ; with four or five flat 

 volutions, almost entirely exposed ; internal margin of the 

 volutions flat, perpendicular to the sides ; ambit broad and 

 flat ; aperture oblong and rectangular. Greatest diameter 

 seven inches and a quarter. 



Found in the Limestone at the Black Rock, Ireland. 



140. A. MULTicosTATUS The Many-Ribbed Ammonite, 



pi. XVIII. fig. 6. 



Ammonites multicostata. Sowerby, Min. Conch. V. p. 76, 

 pi. 454. Fleming, Brit. An. p. 247. De la Beche, Geo. Manuel, 

 p. 375. 



Discoidal, much depressed ; carinated, with three or four 

 entirely exposed volutions ; crossed by numerous, strong, 

 sharp, slightly bent ribs, which are suddenly curved forward, 

 with a depressed, blunted, oblong tubercle on the outer 

 extremity of each, and extending over the ambit almost to 



