ORGANIC REMAINS. 



335 



has been continued to the present time, the same bony and 

 cartilaginous forms, of this class. Their teeth, scales, and 



Ull Ul iH'iiii^. BtwrJ prawn llit mm lia unininin pel itjl Hung, 



at the present hour, those duties which are assigned to them 



CLASS V. FOSSIL MOLLUSCA. 



As we have before observed, the study of fossil shells forms 

 the most important branch of geological inquiry ; because they 

 are often met with in so perfect a condition, and having all 

 their parts so distinctly developed, they serve as, perhaps, the 

 most certain criteria by which to judge of the different strata 

 in which they are found imbedded. The perfection of these 

 shells, in some degree, compensates for the total want of their 

 animal inhabitants in a fossil condition ; but many of these bear 

 such a close analogy to (hose now living, that we may infer 

 their inhabitants were nearly allied to existing species, and 

 that their formation must have been similar. For a classifica- 

 tion of these,and their generic characters, we refer to the article 

 Conchology, and for the characters of the animals, to Mollusca, 

 a term which has, by recent naturalists, been rendered in 

 Knulish Mollusks. 



The whole figures of the class Mollusca refer to plate LXVI. 



ORDER II. CEPHALOPODA. 



DIVISION III. CEPHALOPODA FOLYTHALAMA. 



FAMILY i. AMMONACBA. 



Septa sinuous, lobed, and cut at the margins, meeting together 

 upon the inner wall of the shell, and articulated by jagged 

 sutures. 



BACULITES. Shell straight, cylindrical, sometimes a little 

 compressed, slightly conical ; the walls articulated by sinu- 

 ous sutures; septa transverse, close, imperforate, lobed and 

 lacineate at the margins. 



Baculites Faujassi. PI. 66. f. 1. Erect, cylindrical, opposite 

 sides smooth and depressed ; sutures with lobed dentations. 

 Found in Mount St Peter, at Maastricht. 



HAMITES. Fusiform ; hooked or bent into two parallel limbs, 

 chambered; septa undulated at their margins, with asiphuncle 

 at their outer edge. 



Hamites compressus. PI. 66. f. 9. Depressed, curved at 

 right angles; undulations very regular, sharp, slightly waved, 

 bending towards the curve, and most prominent at the back. 



TURHILITES. Spiral turreted, volutions contiguous, and all 

 conspicuous; partitions articulated with sinuous sutures; septa 

 transverse, lobed, and laciniated at the margin ; siphuncle placed 

 near the upper part of the volutions; aperture nearly round. 



Turrilites tuberculata. PI. 66. f. 2. Volutions beset in the 

 middle with one row of large obtusely conical tubercles, and 

 three rows of smaller ones at the base of each volution. Found 

 in the marl stratum at Middlesham, parish of Ringmer, 

 Sussex. 



AMMONOCBRAS. Horn-shaped, arcuate, subsemicircular; the 

 walls articulated with sinuous, laciniate, branched sutures; 

 septa transverse, sinuous, imperforate ; their margins lobed, 

 laciniate ; a marginal tube or syphon, not perforating tlie septa. 

 Ammonoceras elossoideus. PI. 66. f. 3. Large, thick cylin- 

 drical, arcuated, lateral, depressed ; inside flatly concave ; apex 

 compressed, tongue-shaped ; nineteen inches two lines long. 

 Found in the East Indies, and in Mount St Catharine, near 

 Rouen. 



ORBULITES. Subdisciform, spiral, with the volutions conti- 

 guous, the last enveloping the rest; the inner walla articulated 

 by sinuous sutures ; septa transverse, lobed at their circumfer- 

 ence, and perforated by a manrinal tube. 



Orbulites striatus. PL 66. f. 4. Umbilicated ; volutions 

 hidden ; transversely and minutely btriated and ribbed ; back 

 acute. One and a half inch long. 



AMMONITES. Discoid, spiral; volutions contiguous, and 

 wholly visible ; inner partitions articulated by sinuous sutures ; 

 septa transverse, lobed at the circumference, and imperforated 

 at the disc ; but perforated by a marginal siphuucle near the 

 margin. 



Ammonites Planatulus. PI. 66. f. 5. Smooth, destitute of 

 striae or ribs. 



SCAPHITES. Concamerated, commencing with a depressed 

 volution, with its labt turn enlarged and elongated, and after- 

 wards inflected. 



Scaphites equalis. PI. 66. f. 31. Involute, umbilicated, inner 

 volutions concealed ; surface with produced radii extending all 

 round the volution; outer part rounded with about two pro- 

 jecting striae between, and equal to each of the rays; outer 

 volution ventricose, with greatly enlarged radii, and abruptly 

 terminating without reaching the edge. '1 he external surface 

 has a nacred lustre. Found at Yeovil, In the green sand for- 

 mation. 



ELLIPSOLITHES. Univalve, elliptical, involute chambered, 

 with all the volutions apparent ; aperture lunulate on account 

 of receiving in its inner part the return of the volution. 



EUipsolithes funitus. PI. 66. f. 32. With numerous trans- 

 verse, simple ridges, and intervening grooves somewhat wider 

 than the breadth of the ridges ; a kind of constriction appears 

 at intervals, and distinguished by a small protuberance on the 

 inner part of the rising immediately beyond it. 



FAMILY II. NADTILACEA. 



Shell disciform, with a central spire, and short cells, which 

 do not extend from the centre to the circumference. 



SECTION I. WITH CELLS. 



NAUTILUS. See article Conchology for the generic cha- 

 racter. 



Nautilus striatus. PI. r,G. f. 30. Slightly depressed ; umbi- 

 licus large, exposing a small portion of the inner volutions ; 

 strongly striated concentrically; aperture orbicular, and nearly 

 half the diameter of the shell ; volutions gibbous, few, and 

 increase rapidly. Found in the blue lias at Lyme Uegis, Dor- 

 setshire. 



NUMMULITES. Lentiform, attenuated towards the margins ; 

 spire internal, disciform, multilocular, covered over by several 

 tables ; the outer u all of the volutions complicated, extending 

 and uniting on each side at the centre of the shell ; cells very 

 numerous, small, alternate, and formed by transverse imperfo- 

 rate septa. 



Nummulites complanata. PI. 66. f. 115. Smooth, round, 

 very broad, and flat, with an undulating margin. This species 

 is easily distinguished by its extreme thinness, and all the 

 volutions and every septum being perceptible on the surface. 

 Fig. 7. is a section of an unknown species. Found in the 

 neighbourhood of Saissons, in France. 



VORTICIALIS. Discoid, spiral, multilocular with contiguous 

 volutions, which are not visible externally; provided with 

 imperforate transverse septa, which do not extend from the 

 centre to the circumference ; aperture marginal. 



Vorticialis strigilatn. PI. G6. fig. 10. Somewhat depressed ; 

 spirally ribbed, and spirally striated. 



POLYSTOMKLLA. Discoid, multilocular, with invisible volu- 

 tions, and numerous transverse ribs; aperture formed by vari- 

 ously disposed holes. 



Pclystomella crispa. PI. 66. f. 11. Slightly wrinkled and 

 ribbed transversely. Found in the chalk formations. 



SIDEEOHTES. Discoid, multilocular; volutions contiguous, 

 but not visible externally; disc conoid on both sides, and stud- 

 ded with tubercular dots ; the circumference margined with 

 unequal radiating lobes ; septa transverse, imperforate ; aper- 

 ture distinct, somewhat lateral. 



Siderolites calcitrapoides. PI. 66. f. 12. With four lobes, 

 find punctuated throughout. Found in the mountain of St 

 Peter, at Maastricht. 



Disco RBIS. Discoid, spiral, multilocular, with simple parti- 

 tions; the volutions wholly visible, exposed and contiguous; 

 with transverse, numerous, and imperforate septa. 



Discorbis vesicularis. PI. 66, f. 13. Volutions nodulous, 

 subvesicular ; the internal ones hidden by the nodules. Fouud 

 at Grignon. 



SECTION II. WITHOUT CELLS. 



BELLEROPHON. Involute, and almost spherical, the last vo- 

 lution enveloping the others ; aperture arched, and terminated 

 by the extremities of the columella or axis, and provided with 

 a sinus in its outer edge. 



Bellerophon cornu-Arietis. PI. 66. f. 28. Very thick, 

 somewhat compressed ; internal volutions few, suddenly en- 

 larging and carinated near the aperture, which is considerably 

 expanded ; sinus large and angular. Found in limestone at 

 Kendal, Westmoreland. 



FAMILY III. RADIOLACEA. 



Discoid with a central spire, and elongated radiating cells, 

 extending from the centre to the circumference. 



PLACENTULA. Orbicular, convex above and below, multilo- 

 cular ; aperture oblong, narrow, disposed like a radius iu the 

 lower disc, or sometimes in bo f ,h upper and under. 



Placentula astricans. PI. 66. f. li. Volutions convex, par- 

 titions radiating from the centre ; back undulated, iu conse- 

 quence of a hollow at each partition. 



LENTICULINA. Sublenticular, spiral, multilocular; outer 

 margins of the volutions complicated, and extending above and 

 below the centre ; septa imperforate, curved, and lengthened 

 on both sides in the form of rays ; aperture narrow, projecting 

 over the last volution. 



Lenticulina rotulata. PI. 65. f. 15. Orbicular ; margins 

 acute; disc globular. Found at Mendon. 



ROTULITES. Orbicular, multilocular, spiral convex, or coni- 

 cal above ; fiat, radiated, and tubercular beneath ; aperture 

 marginal and trigonal. 



Rotulites trachidiformis. PI. 86. f. 16. Conoid; volutions 

 carinated; lower one granulated. Found at Grignon. 



FAMILY IV. SPUERULACEA. 



Shell globular, spheroidal, or oval ; with the volutions 

 mutually enveloping, or the cells contiguous, and forming a 

 tunic. 



MELONIA. Subspherical, multilocular; spire central; volu- 

 tions contiguous, convolute, tuuiciform ; cells numerous, 

 narrow ; septa imperforate. 



Melonia Spfusroidea. PI. 66. f. 17. Entirely globular, and 

 divided by depressed ribs. 



GYROOONA. Spherical, concave within, composed of linear, 

 curved canaliculate* pieces; the external surface with carinated, 

 parallel, partly transverse ribs, and bound at the last volution; 

 aperture round, terminated by a small round shell. 



