CONCHOLOGY. 



ni'us.'wRo firft formed this genus in his work, dePolytha- 

 laiiiiis, propolis nine kinds; thefe are divided into two 

 leflions, viz. ift, thofc that liave the iiphiuiculus placed 

 on or near the edge ; and 2diy, tholl- that have it central, 

 tjr near the center. It is proper to oblcrve, that thefe 

 fofTils are almolt always calts of ftonc, or replacements 

 of fparry matter. For a view of the orthoceros, fee the 

 Conchology-Plate II. inhere fig. i reprefer.ts the recent 

 Ihell, cut open, to (hew the concamerations or chambers : 

 this (liell is greatly magnified ; but a figure nearly of its 

 natural fize is placed by its fide. Fig. 2, a fragment of 

 a fo(Hl orthoceros, (hewing- its fiphunculus or pipe of 

 communication, which in both thefe figures is in the cen- 

 ter. This- fragment belongs to a very large fpecies, 

 though it is here (hewn on a linall fcale. 



LITUUS, THE CROZIER. 

 This (hell much refembles a bi(hop's crozier in (liapei 

 having a long cylindric item, one end wliereof turns in a 

 ipiral manner; but the fpires are few, feparated, and re- 

 cede from each other. Breynius defcribes and figures a 

 fnigle fpecies, fo that it is an extremely rare foffil. But 

 there is a fniull recent (hell, commonly called the ram's 

 torn, or nautilus Ipirula of Linnreus, found in great 

 abundance both in the Halt and Welt Indies, which is 

 raniced by mO(t authors as a nautilus or ammonis, and is 

 the identical fpecies with the follll kind. We only fee 

 the fpiral end of this recent Ihell in our colleiHons, and 

 never with its Item. However, the view alone of it 

 evinces its analogy; for as the fpires are few, and greatly 

 recede from each other, it mult follow that the outer 

 fpire will at ialt infenfibly fall into a ftraight line or a 

 ftem : and the reafon we never find it with the fteni, pro- 

 bably, is owing to the thinnefs and brittlenefs of the 

 fliell ; fo that the agitation of the waves, for it is only 

 found cafr up on the Ihores, eafily breaks o(f this Item or 

 cylindric part. Fig. 3, in the engraving, (liews the entire 

 fliell ; and fig. 4., is the fame cut open, to fliew its cham- 

 bered Itruilure. 



TURBO POLYTHALAMUS, or CHAMBERED 

 TURBINE. 



This genus was founded by Da Cofta. It is only found 

 folTd i and even in that (tate but one fpecies is known. 

 It is a turbinated or fpiral (hell, of a produced or length- 

 ened fliape, exai5tly like a buccinum in appeaiance, but is 

 cor.camerated or chambered, and the diaphragms or par- 

 titions are cut and jagged, like the foliaceous futures of 

 the ammonia. Calts of llone of this kind are found in 

 Dorletfhirc, France, and Swilferland, but never in any 

 great degree of perfeiiiion. Fig. 5, in the engraving 

 fliews a turbo polytlialamus, of the lize ufually found in 

 0orl'et(hire. 



CORNUA AMMONIS, or AMMONIA. 



The (hells of this genus are perfeit helices, the fpires 

 ufually lying between two flats or levels. The fpires are 

 cylindric, and connefted to each other. They gradually 

 diminilh or taper, on both levels equally alike, from the 

 circumference to the center; lb that by the gradual ta- 

 pering of the fpires to the center, the centers of- both 

 flats are concaves. The inner (lru6ture is chambered ; 

 but the diaphragms, or partitions of the cells or cliam- 

 bers, are not roundiOi and with an even edge, as thofe of 

 the orthoceros and nautilus, but are flalhed, or jagged, 

 into procelfes or appendages, which laid together tally 

 and ciofe into one another lb itrongly and cunoufly, that, 

 when joined, the flats or furfaces of the whole ammonis 

 are embelliftied with a beautiful leaved work, exai^ily fi- 

 milarto that on the fcuils of animals : and this by fodilo- 

 gilts is called tlic foliaceous futures ot the ammonites. 

 But this (oliaceous work does not (eem to be a particular 

 cliarafter of the ammonia, for the turbines concamcrati, 

 or preceding genus, have it; and there are fpecies of Of* 

 thocerutitic utid foilll nautili witli. tiie iame work. 



The fiphunculus, or pipe of communication from cham- 

 ber to cliamber in the ammonia, leems to be placed oa 

 the back of the fpires, and not near the edges, or in th« 

 center of them ; but, as this conclulion is drawn from 

 fo(ril rtiells, which are very rarely (o perfeel as to (hew the 

 pipe diftinflly, we mult yet remain uncertain in regard to 

 ioine of their particular charadters. It is however, * 

 matter of allonilhment, thatin this and other families of 

 teltacea, in general the mott common folTil fliells are the 

 Icarcelt in the recent ftate, and vic-e werfa. It could be 

 readily explained, were all the iolTil kinds, not known re- 

 cent, reckoned pelagian (hells, as the ammonia certainly 

 are: but then what reafon can be given for the limpets, 

 fea ears, volutes, cowries, &c. which, though in extreme 

 plenty recent, are very rarely found fofiil, with many 

 other parallel inltances. The foifil ammonia, or ammo- 

 nitx, are found in great abundance, and of many fpecies, 

 in moll parts of the world ; from the (Vnall fize of a pea, 

 through all the gradations of fizes, to above a yard in di- 

 ameter, and proportionably thick. Thefe are not objefts 

 that efcape the eye by their minutenels ; yet, neverthelefs, 

 all the living fpecies of them Hill remain to be difcover- 

 ed, except one very minute kind. This living fpecies of 

 ammonis is (o very minute, as hardly to exceed the big- 

 nefs of a turnip feed, and does not weigh the hundredth 

 part of a grain ; therefore demands the aid of the mi- 

 crofcope to examine it. It was found by Plancus with 

 the recent orthocerofes above-mentioned in the fea-fedi- 

 nient at Rimini ; he has defcribed and figured it in his 

 work. l.innEEUs ranks it among the nautili. It is very 

 remarkable, that this recent fpecies is a diliin£l kind fronv 

 any of the folhl ones known. It not only differs in par- 

 ticular circumltances, but even in an efltmtial chara6ter ^ 

 which is, that as all the folfii ones, or ammonit:£, have .1 

 concave center, this recent kind has a very prominent or 

 projefting one. 



Da Colta has fixed the fpecific iharafters of the foffi! 

 ammonitse, to be taken from the work on the back of 

 their Ipires ; as being the molt obvious, conltant, regular, 

 and certain dillinilion. On this charafter be divides the 

 ammonia into eight claiTes, viz. i. Ammonia whole 

 backs are quite fmooth and plain : ammonia doi fo Uevi. 2. 

 Ammonia whofe backs are llriated, fulcated, or ribbed: 

 ammonia dorib Itriato, (ulcato, vel collato. 3. Ammo- 

 nia that have a plain prominent ridge along the back : 

 ammonia limbo prominulo per totum dorlum duiito. 4. 

 Ammonia with a plain prominent ridge between two fur- 

 rows : ammonia limbo prominulo inter duos fulcos eredto. 

 5. Ammonia with a prominent ridge, not plain, but 

 wreathed or twilled like a rope: ammonia limbo taenio- 

 latu. 6. Ammonia with a plain furrow or channel along 

 the back: ammonia fulco unico per dorfum dufto. 7. 

 Ammonia whofe backs are lludded or fpiked : ammonia 

 dorfo tuberculato vel aculeato. 8. Ammonia whofe 

 backs are deeply notched or toothed like a faw : ammonia 

 dorlb dentato. Thei'e include all the lofllil kinds hithertsx 

 difcovered. Fig. 6, in the copper-plate, reprefents the 

 cornu ammonis, in its entire foHil (late, as found at Diay- 

 cot, ill Wiltfhire. Fig. 7, is the fame fliell, cut open to 

 Ihew its chambered ftrufture. 



AMMONOIDES. 



The definition of this genus is, that, in all other re- 

 fpe6ls except (liape, it relembles the ammonitse ; tor thefe 

 bodies are quite globofe like nautili, and not fl it like am- 

 nionitx. 1'he outer fpire alone makes above one half of 

 the body ; and all the other fpires are very (mail, and ta- 

 per into a concavity, fo that the center is deeply hollow- 

 ed or umbilicated. Liniijeus dalles thefe among his nau- 

 tili. Thefe elegant fuflils are found with the preceding, 

 at Draycot In Wiltfliire, and in Swilferland. Fig. 8, in 

 the engraving, is an exacl delineation of this curious fliell. 



The nautilus. 



The nautili are defined to be (hells, whofe fpires never 



iq>pea[ 



