MOLLUSCA. 



669 



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



shells. Those which, like the Nautilus, have the 

 septa smooth and simple, and the siphon either 

 penetrating the centre of the chambers or running 

 along the inner margin, are grouped into the 

 family Nantilida;, the principal genera of which are 

 Nautilus, Clymenia, Campulites, Litiiites, and Ortho- 

 ceratites. Those, on the other hand, which have 

 the septa sinuous and with lobated margins, and 

 in which the siphuncle runs along their outer 

 margin (in some instances, however, near their 

 centre) are grouped into tlie family Ammonitida', 

 of which the principal genera are Ammonites, 

 Baculites, Hamites, Scaphites, and Turrilites. 



The following tabular arrangement will bring 

 this classification at once under the eye. 



I. — Okdee Dibbanchiata. 

 Tribe A. — Octopoda. 



Family 1. Testacea 



Fio. S — Pearly Nautilus; with the shell laid open; ^ teiitncula; f, fun 



nel ; p, foot ; tti, portion of mantle ; o, eye ; g, Biption. 

 Tribe B. — Decapopa. 

 Family 1. Teuthida:, Calamaries 

 Loligo 



Onychoteuthis 

 Sepiola 



Argonauta 

 Bellerophon ? 



Family 2. Nuda. 



Octopus 



Family I. Cranchia 



Loligopsis 

 Family 2. Scpiadce, Cuttle-fishes 



Sepia 



Family 3. Spinilidce 

 .Spirula 



Family 4. Belemnitidce 

 Belemnites 



Family 1. Kautilidi.c 

 Nautilus 

 Clymenia 

 Campulites 



II. — Ohder Tetbabranchiata. 

 Family 1. Lituites 



Orthoceratites 

 Family 2. Ammonitida} 

 Ammonites 



Family 2. Baculites 

 Ilamites 

 Scaphites 

 Turrilites 



It may be well to add, with reference to the family of Camerines (the Foraminifera of D'Orbigny) with which 

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

 its true place in the animal scale cannot be determined until more shaU 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 

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



the clas.'iification of all MoUusea ought to be primarily based on the structure of the animals the 



characters of the shell, however useful for recognition, not being thoBe 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 Mollusca. Many changes in the classification of Cuvier have been proposed, the grouping of the 

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

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

 animals included in the Cuvierian group of Acephala 7t7ida, but also a large and important assemblage 

 of compound animals hitherto ranked as Zoophytes, viz. — the Bri/ozoa. Referring to the Appendix to 

 the Radiata 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 tlie latter. 



The ordinary Tunicata are divided by Professor JMilne Edwards, who has made them an object of 



