44 INVERTEBRATE ANIMALS. 



it occasionally ascends, and has been seen in shoals 

 floating on the surface after a storm. 



IT Examples of Nautilus pompilius, N. umhilicatus, 

 N. macromphalus, and of a few fossil forms. 



Upper Compartment. 



Sections of the shell to shew the chambers and the 

 siphuncle. Specimen in liquid of the animal 

 within the shell. 



Order DIBRANCHIATA. Gills two ; arms, 

 with suckers. 



Section DECAPODA. Arms ten. 



Group 127.— Genus SPIRULA and allies. The shell of 

 /Spw'M^f'^ is internal and chambered. Estimated number 

 of species : recent, 4 ; fossil, a few, from the lower 

 Tertiary. 



Upper Compartment. 



^ Spirula in spirits with the animal entire, very rare. 

 Section shewing the ventral siphon passing through 

 the chambers of the shell. 



Group 128.— Family BELEMNITID^. /Se'Af/xvov, a dart. 

 Belemnites. Belemnoteuthis Actinocamax. The shell is 

 internal and chambered, and is protected posteriorly by 

 a cylindrical guard tapering to a point. This guard is 

 the only part commonly found. Estimated number of 

 species 40, all known as fossils, chiefly from the Lias. 



H Specimens from Dr. Mantel's collection, in very 

 fine condition, shewing the horny pro-ostracum, 

 the ink-bag, and the phragmacone. 



