316 



Cephalopoda. - 



-MOLLUSCA.- 



-Nautilid.e. 



into the uumeroiis cells of this shell, thus at ■will var}'- 

 iiig their proportionable weight to the sea in which they 

 live ; and M. d'Orbigny is of opinion that the use of 

 the pror .inent mucro, or point, is to protect the animals 

 in the frequent collisions they are exposed to in swim- 

 ming backwards. The black liquid secreted by this 

 species of Cuttle-fish is said to form at least the greater 

 jiortion of the colour called sepia. Though now it is 

 pretty well ascertained that the China ink of commerce 

 is prepared from lamp-black or finely triturated char- 

 coal, it was long believed to be furnished by this 

 secretion ; and Cuvier tells us that an ink is still pre- 

 pared from this secretion in Italy, which only ditl'ers, 

 he says, from genuine China ink in being a little 

 less black ; and that it was with this preparation he 

 drew the designs which illustrate his memoir on the 

 Mollusca. The hone, as it is called, or shell of the 

 Sepia, is much used in the preparation of tooth-powder 

 and pounce. It was formerly employed by medical 

 men as an antacid, but is now little esteemed for 

 that purpose. It is of more value, when powdered, 

 fur making moulds for silversmiths for casting articles 

 of small work, such as spoons, forks, and rings. 



Section III.— BELEMNOPHORA. 



This section contains only one recent family : — 



Family— SPIRULID^ {Splrulas). 



These animals have an oblong body, with minute 

 terminal tins. The sessile arms have six rows of very 

 minute cups, and the tentacular arms are elongated. 

 The shell is entirely nacreous, discoidal, with the whirls 

 separate, and chambered, the chambers furnished with 

 a siphon. The last chamber is only large enough to 

 contain a very small part of the animal ; the rest of the 



shell being placed vertically in the posterior part of the 

 body, with the involute spire towards the ventral side. 

 However dissimilar, says Cuvier, this shell is in figure 

 to the bone of the sepia, it does not differ much from 

 it in the manner of its formation. "If we imagine 

 that the successive layers, instead of remaining parallel 

 and in nigh approximation, were to become concave 

 towards the body, more distant, each growing a little 

 in breadth, 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 Spirula, which has 

 tliese additional characters, that the turns of the spire 

 do not touch, and that a single hollow column, occu- 

 pying the interior side of each chamber; continues 

 its tube with those of the other columns even to the 

 extremity of the shell. This is what is named the 

 SiphonJ" 



Genus Spirula (^Litmis). — The family contains 

 only this one recent genus. Though the shell of 

 Spirula has long been well known, specimens of one 

 of the species being often found brought by the gulf 

 stream, and thrown up on the shores of our own 

 country, and thousands of them scattered along those 

 of New Zealand, yet the animal has been very seldom 

 seen. An imperfect specimen was brought home some 

 years ago by Captain (now Admiral) Sir E. Belcher, 

 and served Professor Owen as the f pecimen from which 

 his memoir on the anatomy of the creature was drawn 

 up; and more recently a nearly perfect specimen of 

 another species has been found by Mr. Earl oil' the 

 coast of New Zealand, which is now in the possession 

 of Mr. Cuming, and was figured by Mrs. Gray in the 

 Annals of Natural History, vol. xv. From the little 

 we know of its habits, it is most probable that the 

 Spirula is pelagic, and swims near the surface in calm 

 weather towards evening, preying on acalephse, and 

 sinking below the surface during the day. Three 

 species have been described. 



Order II.— TETRABRANCHIATA. 



The animal in this order of Cephalopods creeps instead 

 of swims, and has its body protected by a shell. The 

 body is destitute of fins, and is attached to the, shell 

 (unlike that of Aryonaiila) by adductor muscles, and 

 by a continuous horny girdle. The head is retractile 

 within the mantle, is not separate from the body, and 

 is surrounded by a great number of cj'lindrical, annu- 

 lated, retractile tentacles, destitute of suckers. The 

 eyes are slightly pedicelled, the mandibles are calcare- 

 ous, the siphuncle, or funnel, is slit ; and, as the name 

 of the order indicates, they have four gills or branchije. 

 The shell is external, chambered, and is provided with 

 a siphuncle. "The inner layers and septa are nacre- 

 ous, and the outer layers porcellaneous." — Woodward. 

 This order contains three families, only one of which, 

 however, possesses any recent species. 



Family— NAUTILIDiE {The Nautili). 



This family contains but few living representatives, 

 but in former periods of the earth's history they 

 appear to have been extremely numerous. 



Genus Nautilus. — This is the only genus belonging 

 to the fomily. The tentacles which surround the head 

 of the animal are very numerous. On each side of the 

 head there is a double series of arms or brachial tentacles, 

 as they are called, thirty-six in number, lamellated on 

 their inner surface, and retractile within l^heaths or digi- 

 tations which correspond to the eight ordinary arms uf 

 the Dibrancliiate species. There are also four groups of 

 labial tentacles, twelve or thirteen in each group, wliich 

 I appear to answerto the buccal membrane of the ordinary 



