314 MOLLUSCA. 



much more various, as to form, than those now taken in the 

 ocean(l). 



Chambered shells are also found among fossils, furnished with 

 simple septa and a siphon, the body of which, at first arcuated or 

 even spirally convoluted, remains straight in the more recent partsj 

 they are the Lituus of Breyn, in which the whorls are sometimes 

 contiguous(2), and sometimes distinct the Hortoles of Montfort. 



In others, the ORTHOcEiiATiTEs(3), it is altogether straight. It is 

 not improbable that the aniinal resembled that of the Nautilus or 

 of the Spirula. The 



Belemnites 



Probably belong to this family, but it is impossible to ascertain the 

 fact, as they are only found among fossils; every thing, however, 

 proves them to have been internal shells, thin and double, that is, 

 composed of two cones united at base, the inner one much shorter 

 than the other, and divided into chambers by parallel septa, which 

 are concave on the side next to the base. A siphon extends from 

 the summit of the external cone to that of the internal one, and con- 

 tinues thence, sometimes along the margin of the septa and some- 

 times through their centre. The interval between the two testaceous 

 cones is filled with a solid substance here composed of radia- 

 ting fibres, and there of self-involving conical layers, the base 

 of each being on the margin of one of the septa of the inner 

 cone. In one specimen we only find this hard portion, and in ano- 

 ther we also find the nuclei of the chambers of the inner cone, or 

 what are termed the alveoli. Most commonly these nuclei and the 

 chambers themselves have left no other traces than some projecting 

 circles on the inside of the internal cone. In other specimens again 

 we find more or fewer of the nuclei, and still in piles, but detached 

 from the double conical sheath that enveloped them. 



Of all fossils the Belemnites are the most abundant, particularly 

 in chalk and compact limestone(4). 



(1) Large species, with a single siphon; the Anguiite, Mont., f. 1, 6; the 

 Aganide, Id., 50; the Cantrope, Id., 46. 



(2) Nautilus lituus, Gm. ; Naut. semilituus, Plainc, I, x. 



(3) Breyn. de Polythal., pi. iii, iv, v, and vi; and Walch, Petrif. of Knorr., 

 Supp. IV, b, iv, d, iv. See also Sage, Journ. de Phys. an. IX, pi. 1, under the 

 name of Belemnite. 



(4) The best works on this singular genus of Fossils, are the Memoires sur les 

 Belemnites constderees zoologiquement et geologir/uement, by M de Blainville, Paris, 

 4to, 1827; and that of M. J. S. Miller on the same subject in the Geol. Trans., se- 

 cond series, vol. II, part I, London, 1826. See also Sage, Journ. de Phys. an. IX, and 



