102 



THE CEPHALOPODS. 



the branchiae and viscera. The mantle is open, in some 

 genera, along its entire outline, when it forms two distinct 

 compressed lobes; in others, it is open at its two extremities 

 only; and, in others, the apertures are confined to one end. 



V. Brachiopods. — This class embraces the m oil usca which, 

 enclosed likewise in a mantle, and without any distinct head, 

 have a pair of labial fleshy or membranous arms fringed with 

 cilia of the same nature. 



The first class or Cephalopods comprises only one order 

 (which it was therefore unnecessary to name), divided into 

 genera, of the same value as the families of subsequent syste- 

 matists, from the character of the shell. The typical genus 

 — the Sepias — has no outer shell, excepting in the instance 

 of the Argonauta, the cuttle of which Cuvier regarded as 



its proper fabricator ; but the greater 

 number of the other cuttle fish have 

 an interior lamellated cellular, or 

 sometimes horny, plate, formed in a 

 peculiar cavity in the back. This 

 genus embraces the Octopus or Po- 

 lypus of the ancients ; the Loligo 

 (Fig. 12), or Calamary, which have 

 two additional arms longer than the 

 proper feet; and the Sepia, properly 

 so called. The Nautilus, embracing 

 all the spirally intorted many-cham- 

 bered shells, is the second genus, of 

 which the N. pompilius is the most 

 familiar and characteristic exemplar. 

 The third is the Belemnites, — coni- 

 cal straight multilocular fossils of a 

 very singular structure, which de- 

 cides them to have been the internal 

 supports of probably the most extra- 

 ordinary constituents of the class in 

 an epoch of foregone time when all 

 was strange ; and now they appear to us anomalous and 

 monstrous. It is upon well-grounded conjectures that the 

 fossil Ammonites are also located here, distinguished from 

 the Nautilus by the partitions between the chambers, which, 

 instead of being plain or simply concave, are angulated, 

 sometimes wavy, but more commonly laciniated on their 

 margins, so as to resemble the crisping of the leaves of 

 the acanthus.* They are believed to have been likewise 



* The inner structure is chambered, but the diaphragms, or partitions 



