INVERTEBRATE ANIMALS. 43 



Order DIBRANCHIATA. gills two; arms, 

 with suckers. 



Section DEC APOD A. arms ten. 



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



Spirilla is internal and chambered. Estimated number 



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



Tertiary. 



Upper Compartment. 



IT 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^. (5l\siJ,vov, 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. 



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



fine condition, shewing the horny pro-ostracum, 



the ink-bag, and the phragmacone. 



Group 129.— Family SEPIAD^. Cuttles. 2»]7r/a. 

 Aristotle, from o-jTrurj, a pouch. The shell is internal, 

 consisting of an oval calcareous plate, shewing at the 

 apex traces of the chambered structure characteristic 

 of the order. Estimated number of species : recent, 

 30 ; British, 3 ; fossil, 9. Oxford clay, &c. 



IT Fossil remains and recent specimens of cuttle- 

 bone. 



Upper Compartrfient. 



Coloured drawings of the animal, and preparations 

 in liquid. 



