MOLLUSCA. 



669 



fu?sil I 



sof this order are very numerous, raitl ar 



iod accoivlhiij; to tho stfucture of tlieir chambered 

 shells. Those -whiLOi, like the Navtllu?., have the 

 septa Bmooth ami simple, and the siphon either 

 penetrating the centre of the eharabers or running 

 along the inner margin, are grouped into the 

 family NanUlickv, the principal genera of which arc 

 Nautilus, C{ymenia, CampuUtes, Lituites, and Ortho- 

 ceratites. Those, on the other hand, which have 

 the septa sinuous and with lobated margins, and 

 in which the sipJiuncle runs along their outer 

 margin (in some instances, however, near their 

 centre) are grouped into the family Amrnonitidci:, 

 uf which the principal genera are Ammonites, 

 Baculites, Uamitcs, Scaphitcs, and Turrilites. 



The folloiviug tabular arrangement will bring 

 this classitication at once under the eye. 



I. — OKDER DlBBANCHlATA. 



Tribe A. — Octopoda. 



Fri5. !y — Pearly Mautilu: 



Tribe B. — Becapoda. 

 Family 1. Tentlildcr, Calamaries 

 Loligo 



Onyehoteuthis 

 Sepiola 



Family 1. Navtilidm 

 Nautilus 

 Clymenia 

 Campulites 



rh the shell Ink! open ; I, fciitncula; i 



Family 1. Testa^ca 



Argonauta 

 Bellerophon ? 



Family 2. Niid-a. 



Octopus 



Family 1. Oranchia 



Loligopsis 

 Family 2. SepiadcB, Cuttle-fishes 



Sepia 



Family 3. SpirulicliE 



8pirula 

 Family 4. BelemniUdcB 

 Belemnites 



II. — OeDEB. TETBABItANCIIIATA. 



Family 1. Lituites 



Orthoceratites 

 Family 2. Awmonitidce 



Ammonites 



Family 2. Baculites 

 Ilaniites 

 Scapbites 

 TurriUtes 



It maybe well to add, with reference to the family of C'amo-ines (the Foraminifera of D'Orbigny) mth 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 %vliieh the 

 shells arc formed. 



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

 COMCHIFERA, and Brachiopoda. The principle advanced by Cuvier and Lamarck, however that 

 the classification uf all MoUusca ought to be primarily based on the structure of the animals. — the 

 characters of the shell, however useful for recoL^nition, 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 animals of the testa- 

 ceous TMollusca. Many changes in the classification of Cuvier have been proposedj the grouping of the 

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

 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 class Tunicata, chiefly through the re- 

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

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

 animals included in the Cuvierian group of Acepkala nuda^ but also a large and important assemblage 

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

 the Kadiata for an account of the organization of these animals, which differ in some 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 has made them an object of 



