410 THE OCEAN WORLD. 



of all sizes. The most remarkable genera which we shall describe 

 belong to the family of Troehoidw and Buccinoidse. 



The fourth order of Gasteropods, Prosobranchiata, which includes 

 the Pecteni Branchiata, is distinct in the sexes, has the branchiae 

 pectinated, and the mantle forms a vaulted chamber over the back of 

 the head. It is divided into two sections and twenty-one families. 

 The first section, Holostomata, contains the sea-snails. The first 

 family we shall treat of is the Chitonidte, containing Chitondlus and 

 Chiton. 



The Chitons are very singular creatures, desti- 

 tute of eyes, of tentacles, and without jaws ; they 

 bear upon their back in place of a shell a cuirass 

 composed of imbricated and movable scales. They 

 have the power of elongating and contracting 

 themselves like the snails. They roil themselves 

 up into a ball like the woodlouse. They adhere 

 with great force to the rocks, preferring those 

 places most exposed to the beating waves. Chiton 

 maanificus (Fig. 211) is widely distributed. 



Fig. 211. Chiton magnificus J J V b ' J 



(Deshayes). The second family, Dentaliadie, affords the 



curious Dentalium, or tooth shell. 



The Pateliidfe, or Limpets, constitute a very numerous family, dis- 

 tinguished at once by the form and structure of the animal, and by 

 that of the shell. Linnaeus called it Patella, i. e., a deep dish or knee- 

 cap. 



The shells of the Patellidae, our third family, are univalve, oval, or 

 circular, non-spiral, but terminating in an elliptic cone, concave and 

 simple beneath, non-pierced at the summit, entire and inclined an- 

 teriorly. They are smooth, or ornamented on the sides with ridges 

 radiating from the summit, and often covered with scales ; the edges 

 are frequently dentate. The colours much varied. The interior is 

 very smooth, and remarkable for the brilliancy and lustre of its tints. 



The head of the animal is furnished with two pointed tentacles 

 or horns, having an eye at the external base of each. The body is 

 oval and nearly circular, conical, or depressed. The foot is in the 

 form of a thick fleshy disk. Certain lamellar branchiae are arranged 

 in series all round the body. 



The Limpets dwell upon the sea-shore, in the parts alternately 



