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CEPHALOPODA. 



lam. 1. NAUTILIDJZ, Nautilites. 

 Animal, organized as described in the 



character of the order. 

 Shell external; spiral, or straight; septa 

 smooth, and simple ; the last chamber 

 the largest, and containing the animal : 

 siphon central, or marginal and in- 

 ternal. 



EJT. GENERA Nautilus, Lamarck; Cly- 



i/icncs, Munster ; Campulites, Des- 



hayes; Lituites, Breyn; Orthoceratites, 



Breyn. 



Fam. 2. AMMONITID&, Ammonites, 



Snake-stones. 

 Animal unknown, presumed to resemble 



the Nautilus. 



Shell external ; spiral or straight ; septa 

 sinuous, and with lobated margins ; 

 the last chamber the largest and lodg- 

 ing the animal : siphon central, or mar- 

 ginal and external. 



EJC. GEKERA Baculites, Lamarck; Ha- 

 mites, Parkinson ; Scaphites, Parkin- 

 son ; Ammonites, Bruguiere ; Turru- 

 lites, Lamarck. 



The Dibranchiate Order of Cephalopods 

 also had its representatives in the seas of the 

 ancient world, as the shells called Belemnites, 

 or thunder-stones, the fossil shells of the Sepiae 

 discovered by Cuvier, and the horny rings of 

 the acetabula found by Buckland in the fossil 

 faeces of Ichthyosauri, sufficiently testify; but 

 our knowledge of this order is chiefly founded 

 on observation of existing species. These are 

 extremely numerous; they frequent the seas 

 of every clime, from the ice-bound shores of 

 Boothia Felix to the open main, and floating 

 Sargasso or gulf-weed of the Equator; they seem, 

 however, to be most abundant in temperate lati- 

 tudes. Many species frequent the coasts, creep- 

 ing among the rocks and stones at the bottom ; 

 others are pelagic, swimming well, and are 

 found in the ocean at a great distance from 

 land. 



The Dibranchiata present great variety of 

 size, and although the bulk of the gigantic 

 species has been undoubtedly exaggerated, yet 

 the organization of this order is favourable 

 to the attainment of dimensions beyond those 

 presented by the individuals of any other 

 group of Invertebrate animals. The remains 

 of the large Uncinated Calamary caught by 

 Banks and Solander in the Southern Ocean, 

 parts of which are still preserved in the 

 Hunterian Museum, and the fragment of the 

 Cephalopod weighing one hundred pounds, 

 taken by the French naturalists in the Atlantic 

 Ocean under the line, and preserved in the 

 Museum of the Garden of Plants at Paris, 

 afford indubitable testimony of the formidable 

 size to which some individuals of this order 

 attain. 



The species included in the higher divi- 

 sion of Cephalopods very naturally resolve 

 themselves into those which possess the eight 

 ordinary arms, forming the tribe Octopoda ; 

 and into those which have the additional pair 

 of elongated tentacles, forming the tribe De- 

 capoda. 



The Decapods are further characterized by 

 having a pair of tins attached to the mantle; 

 by having the funnel either adherent at the 

 antero-lateral parts of its base, and without an 

 internal valve, or articulated at the same part 

 by two ball-and-socket joints to the mantle, and 

 provided with a valve internally at its apex ; 

 by having fleshy appendages to the branchial 

 hearts, and glandular appendages to the biliary 

 ducts; by having generally a single oviduct, 

 with detached superadded glands ; and, lastly, 

 by the shell or its rudiment being single, mesial, 

 and dorsal. 



The Decapodous tribe is that which is most 

 nearly allied to the Tetrabranchiate Order. This 

 affinity is not only indicated by the additional 

 number of external arms, and the frequent de- 

 velopment of an internal circular series of eight 

 short labial tentacles, but by several internal 

 characters; as the single oviduct and detached 

 glands for secreting the nidamentum ; the valve 

 of the funnel; the laminated rudiment of a 

 chambered shell in the Cuttle-fish, and the fully 

 developed chambered and siphoniferous shell 

 of the Belemnites and Spirilla. The observa- 

 tions of Peron and Lamarck having proved 

 that the animal of the Spirula possesses eight 

 short arms and two long tentacles, all provided 

 with acetabula, like the Sepia, we regard it 

 as the type of the first family of the Decapo- 

 dous Tribe, or that which immediately succeeds 

 the Tetrabranchiata. 

 Tribe DECAPODA. 

 Fam.l. SPIRULIDM. 



Animal, corresponding in external form 

 to the Decapodous type ; internal or- 

 ganization unknown, presumed to be 

 Dibranchiate. 



Shell partly internal ; cylindrical, multilo- 

 cular, discoid ; the whorls separated ; 

 septa transverse, concave next the out- 

 let, and with regular intervals. 

 Siphon marginal and internal, uninter- 

 rupted. 



Genus SPIRULA, Lam. 

 The character of the family is also that of 

 the single genus of which it is at present 

 composed. 



Ex. Spirula Australis, Lam. 

 Fam. 2. BELEMN1TIDM, Belemnites, 



Thunder-stones. 

 Animal unknown.* 



Shell internal, composed of an external 

 calcareous sheath formed by a succes- 

 sion of hollow cones, the exterior being 

 the largest; of an internal horny sheath, 

 also of a conical form, containing at its 

 apex a chambered shell, the septa of 



* As it is certain that the animals of this family 

 of extinct Cephalopods possessed the ink-bag, they 

 must consequently have been enveloped by a mus- 

 cular mantle ; and we may, therefore, infer that 

 they resembled the Dibranchiates in their locomo- 

 tive and respiratory organs, and consequently in 

 the general plan of their organization. In the 

 structure and position of their siphoniferous catne- 

 rated shell they are intermediate to Spirula and 

 Sepia, and as the animal of Spirula is proved to be 

 a Decapod, the probability is very strong that the 

 animal of the Belemnite was of the same type. 



