MOLLUSCA. 



669 



fossil remains of this order are very numerous, and are classed according to the structure of their chambered 

 p t shells. Those which, like thi 



septa smoctli and simple, and the siphon either 

 penetrating the centre of the chambers or running 

 along the inner margin, are grouped Into the 



family NaiUUidcB, the principal genera of which are 

 •--■ e Nautilus, Clymenia, CampuUUt, lAtuitea, and I 



ceratii: .-•. Those, on the other hand, which havo 

 the septa sinuous and with located margins, and 

 in which the siphnncle runs along their outer 

 margin (in some instances, however, near tlnir 

 O centre) are grouped into the family AvmoutUdCB, 



of which the principa] g inera are Amu, 

 Baculites, Ilamitci, SoajphiUs, ami Turrilitcs. 



The following tabular arrangement will bring 

 this classification at once under the eye, 



I. — Order Bibranchiata. 

 Tribe A. — Octopoda. 



Family 1. Testacea 



9 

 Fio. 5. — Pearly NAUTILUS] with the shell laid open; I, tcntncula ; e, fun- 

 nel ; p, foot ; m, portion of mantle ; <j, eye ; g, siphon. 



Tribe B. — Becapoda. 

 Family 1. TeutMdCB, Calamaries 

 Loligo 



Onychoteuthis 

 Sepiola 



Argonauta 

 Bellerophon ? 



Family 2. Nttda. 



Octopus 



Family 1. Cranchia 



Loligopsis 

 Family 2. Sepvidas, Cuttle-fishes 



5* pia 



Family 3. Spirulida; 



Spirula 

 Family 4. Belemnitidce 



Belemnites 



Family 1. Nautttida 



Nautilus 



Clymenia 



Campulites 



Family 2. Baculites 

 Hamites 

 Scaphites 

 Turrilin-s 



II. — Order Tetrabranciuata. 



Family 1. hituites , 



Orthoceratites 

 Family 2. Ammonitidce 

 Ammonites 

 It maybe well to add, with reference to the family of Camerinet (the Foraminifera of B'Orbigny) with which 

 Cuvier's description of this class terminates, that it is now universally rejected from the Cephalopoda, though 

 its true place in the animal scale cannot be determined until more shall be known of the animals by which the 

 shells are formed. 



No very important change has been made in the classification of the Pteropoda, Gasteropoda 

 Con-chifera, and Brachiopoda. The principle advanced by Cuvier and Lamarck, however, that 

 the classification of all Mollusca ought to be primarily based on the structure of the animals, — the 

 characters of the shell, however useful for recognition, not being those on which a natural arrange- 

 ment ought to be founded, — is now generally admitted; and the attention of Naturalists has been of 

 late much directed to the increase of our acquaintance with the anatomy of the animal-; of the testa- 

 ceous Mollusca. Many changes in the classification of Cuvier have been proposed, the grouping of 

 genera into orders being varied according to the principles of arrangement adopted by each systematise 

 But no one classification has met with such general acceptance, as to be entitled to replace that of 

 Cuvier. 



Much has been added, however, to our knowledge of the (lass Tunicata, chiefly through the re- 

 searches of Professor Milne Edwards. And it ia now considered by many Naturalists (See the Histarj 

 of British Mollusca, by Forbes and Hanley, p. 1,) that this class should comprehend, not merely the 

 animals included in the Cavierian group of Acephala mufti, bnt also a large and important assemb 

 of compound animals hitherto ranked as Zoophytes, viz.— the Bryozoa, Referring to the Appendix to 

 the Radiate for an account of the organization of these animals which differ in tome important parti- 

 culars from the ordinary Tunicata, we shall at present confine ourselves to a review of the latter. 



The ordinary Tunicata are divided by Professor Milne Edwards, who DM made them an object of 



