342 



MOLLUSCA. 



fissure ; from the exterior surface being marked with a longitudinal gutter on one side, or with two or 

 several gutters towards the summit ; or as that surface is smooth and without gutters. 



Some fossils, very much like the Belemnites, but without a cavity, and even with a protruding basis, 

 form the genus Actinocamax of Miller. 



It is upon similar conjectures that the classification of the 



Ammonites, Brug., or Snake-stoxes, — 

 Is founded, for they, also, are only found in a fossil state. They are distinguished, in general, from 

 Nautilus, by their septa, which, instead of being plain or simply concave, are angulated, sometimes 



undulated, but oftener gashed on the margins, 

 like the leaves of the Acanthus. The smallness 

 of their last cell leads to the belief that, like the 

 i Spirula, they were internal shells. The beds of 

 the secondary mountains swarm with them, and 

 we find them there from the size of a bean 

 to that of a chariot wheel. The variations 

 of their whorls and of their syphon enable 



Fig. lM.-Ammomlc them tQ ^ suMivided# Thus the name 



Ammonites, Lam., is restricted to the species in which all the whorls are visible. Their syphon 

 is near the margin. They have been still further distinguished into those which have the margins 

 of the septa foliaceous, (the Ammonites, the Planites of llaan,) and into those in which they 

 are simply angular and undulatory (the Ccratitex of llaan). Those in which the last whorl envelopes 

 all the others, are the Orbulites, Lam., or thi - and Gondatites of llaan, or Pehgiues, Monti 



The syphon is the same as in Ammonites.* The name Scaphites, Sowerby, [or rather of Parkinson,] 

 has been appropriated to those - hose whorls are contiguous and on the same plane, excepting 



the last, which is detached and bent upon itself. Those which are perfectly straight are the Baculites, 

 Lam. Some are round, others are compressed ; and in the latter we some- 

 times observe the syphon to be lateral. The Ifamites of Sowerby, [Par- 

 kinson,] are known by having their first formed cells arcuated. But the, 

 Turrilites, Montf., differ more than any from the usual habit of the family, 

 for the whorls, in place of remaining on the same level, descend rapidly, 

 and give to the shell that obelisk form which is denominated turriculated. fu. 155.— portion of a Bac»nte 



From analogy, it is supposed that we ought to refer to the Cephalopods, and to consider as being in- 

 ternal shells 



The Camerines, Brug. (Xummulites, Lam.), — 



For all of them are equally fossil. They have a lenticular shape, without any apparent aperture, but 

 within there is a spiral cavity, divided by septa into a multitude of little clrambers without a syphon. 

 They are amongst the most generally diffused fossils, and almost of themselves form some entire chains 

 of calcareous hills, and immense banks of building stone. (It is upon such rocks that the pyramids of 

 Egypt are founded, and with stones of the same description that they are built.) 



The commonest, and which attains the largest size, are altogether discoid, and have only a single 

 row of chambers in the whorl of the spire. Some minute sorts of this description have been also found 

 recent in some seas. Other minute species, both living and fossil, have their margin bristled with points, 

 which give to them the figure of stars (Siderolit/ies, Lam.). 



The works and the patient researches undertaken successively by Bianchi (or Janus Plancus), Soldani, 

 Fichtel and Moll, and Alex. d'Orbigny, have made known an astonishing number of these chambered 

 and esyphonar shells (Numrmdariai), of extreme littleness, so as often to be altogether microscopical, 

 either in the sea, among sand, sea-weed, &c. ; or, in a fossil state, in the sand-beds of various countries; 

 and these shells vary to a remarkable extent in their contour, the number and the relative position of 

 their chambers, &c. One or two species, the only ones in which the animals have been noticed, have, 

 apparently, a small oblong body surmounted by numerous red tentacula, a structure which, taken in 



* According to Sowerby, Orbulitrs and *4mmonoceras, of Lamarck, are not distinct from Ammonites. The Ammonoceras is only an acci- 

 dentally worn portion ot an Ammonite. — Ed. 



