CEPHALOPODES. 



341 



tliat the successive layers, instead of remaining parallel and in nigh approximation, were to hecome 

 concave tov\'ards the hody, more distant, each growing a little in hrcadtli, and making an angle 

 between them, we should then have a very elongated cone, rolled up spirally on one plane, and divided 

 transversely into chambers. Such is the shell of Spir ila ; which has these additioual characters, that 

 the turns of the spire do not touch, and that a single hollow column, occupying tlie interior side of 

 each chamber, continues its tube wilh those of the otlicr columns even to the extremity of the shell. 

 This is what is named the Syphon. 



Only one species {NaiitUus spirula, Linn.) is known. 



The shell of the Naidilus, properly so called, differs from that of the Spirula in this,— tlint the septa increase 

 very rapidly, and tliat the last turns of the spire not only touch, hut envelope the preceding;. The syphon is in the 

 centre of each partition. The common species ijyanlilu.f pomjuVnis, Lin.) is very lar^e, sihered within, and 

 covered e-\ternally with a whitish ciust, varied with reddish somewhat undulated hands. According; to Rumphius, 

 its animal should be in part lodL,^ed in the last cell, and should have the sac, the eyes, the parrot-like beak and the 

 funnel of other Cephalopods; but its mouth, instead of their great feet and arms, should he surrounded with 

 several circles of numerous little tentacula, destitute of suckers. A li;^ament springing from the beak should run 

 through the syphon, and 11.x the animal to it. It is probable also that the epidermis is prolonged over the exte- 

 rior of the shell ; hut we may conjecture that it is thin upon such parts as are vividly coloured.* 



We meet with specimens of Nautilus {N. pomp'iUus, B. Gm. List. 552; Ammonia, Montf. 74), in whirh the last 

 whorl does not envelope nor conceal the others, hut in which all the whorls, although thfy touch, are visible, — a 

 character which approximates them to the Ammonites ; yet in every other respect they so closely resemble the 

 common species that it is difficult to believe they are not a variety of it. 



Among fossils there are Nautili of large and moderate sizes, and of figures more varied than now exist in the ocean. 



We also find among fossils certain chambered shells, with simple septa and a syphon, in which the body is at 

 first arched, or even spiral, but the last-formed parts of it are straight ; these are the Lituus of Bi-eyn, in which 

 the whorls are either contiguous or separate, (the Hortoles, Montf)— Others remaining straight throughout their 

 growth are the Orifwcerafites. It is not improbable that their animals had some resemblance to that of the 

 Nautilus, or to that of the Spirula. 



The Belemxites 

 Belong, probably, to the same family, but it is impossible to be sure of this, since they are only fouiirl 

 in a fossil condition. Their whole structure, however, shows that they were internal shells. f They 

 have a thin and double shell, that is to say, composed of two cones, united 

 at their base, and the interior of which, much shorter than the other, is itself 

 divided iuternally into chambers by parallel septa, concave on the side that 

 looks to the base. A syphon extends fi'om the summit of the exterior cone 

 to that of the internal cone, and is continued hence, sometimes along the inargni 

 of tlie septa, and sometimes through their centre. The space betm'een the 

 two testaceous cones is filled witli a solid substance, composed either of la 

 diating fibres or of conical layers, which envelope each other, and each of 

 which rests on the margin of one of the septa of the inner cone. Sometimes 

 we find only this solid part ; at other times we find also the nuclei of the cham- 

 bei-s of theinnercone, or whathas been called thealyeote. Oftener these nuch i, 

 and even the chambers, have left no other traces behind than some projectnij 

 circles within the inner cone; and in other instances, the alveolie are found 

 in greater or less numbers, and still piled or strung together, but detached 

 from the double conical case which had inclosed them. 



The Belemnites are amongst the most abundant of fossils, particularly in 

 beds of chalk and compact limestone. The most complete works upon tin ui 

 are the Memoire mr les Bekmnites c-onsideries zoologiquement et gcohrjiqvc- 

 vient, by Blainville, Paris, 1827 ; and that of M. I. S. Miller on the same 

 subject, in vol. u. part 1, of the Geoloijical Trans., Loud., 1826. [The 

 English student will find the fullest details in Buckland's Bridgewater 

 Treatise.] M. de Blainvdle distributes them from characters derived from 

 the greater or less depth to which the inner cone, or chambered part, pene- 

 trates ; from the margins of the external cone, which has, or has not, a small 



lich fossils are occasionally refcrreii t 

 ispall believes the Belemnites to be 

 me sea animal, perhaps allied to the £ 



* The structure of this siii^lar Ccpb.alopod has been fully described 

 md illustrated in a very admirable manner, by Mr. 0,ven, in his 

 ■ .l/e„o.!>on the Pearly NatilUm;' Lotid., 1S32.— En. 



t It may [jive the student an idea of the nature of the evidence on 



appendages 

 i-urchius, C^e/iinus).— f:ij 



