CHITON. 



34. Other cyclobranch gastero- 

 pods, called Chiton (fig. 79), differ 

 from all mollusks, in the nature of 

 their shell, which, instead of a tur- 

 binated or shield-like piece, is com- 

 posed of a row of testaceous and 

 symmetrical scales, generally eight 

 in number, let into the mantle, and 

 occupying the middle line of the 

 back. The edges of this mantle, 

 thus protected, are also very 

 leathery, and often furnished with 

 little scales, spines, or hairs. A 

 membranous veil placed over the 

 mouth, takes the place of tentacles ; 

 the branchiae are composed of 

 Fig. 79. CHITON. lamellar pyramids, arranged on each 



side, beneath the edge of the mantle ; the anus is at the posterior 

 extremity of the body. Chitons most abound on the shores of 

 tropical seas. 



ORDER OF GASTEROPODA INFEROBRASSTCHIATA. 



35. The order of Inferobranch gasteropods is composed of a 

 very small number of naked mollusks, characterized by their 

 branchia3, consisting of a long series of leaflets, placed on each 

 side of the body, between the foot, and the advanced edge of the 

 mantle. Like the preceding, they are marine, and differ from 

 them, not only in the absence of every vestige of shell, but also 

 in some points of their internal anatomy, which approximate 

 them to the gasteropods. They are divided into PHYLLIDIA 

 (from the Greek, phullon, a leaf), in which the anus is posterior 

 to the mantle, and the head is furnished with four tentacles ; 

 and into DIPHYLLIDIA (from the Greek, dis, two, and phullon^ 

 leaf), in which the anus is on the right side, and the head has a 

 pointed tentacle, and small tubercle on each side. In all of them, 

 the body is oval, or more or less tuberculous. 



ORDER OF GASTEROPODA TECTXBHANCHIATA. 



36. The Tectibranch gasteropods are, like the preceding, ma- 

 rine mollusks, but their branchiae are not symmetrical ; they 



34. What are the characters of the genus Chi'ton ? (pronounced Icy-ton.) 

 (Chiton; Greek, a garment.) 



35. How are the In'ferobranch ga'steropods characterized ? (Infero- 

 branch ; from the Latin, inferus, below, and branchiae, gills.) 



36. What are the characters of the tecMlbranch gasteropods ? (Tecti- 

 branch ; from the Latin tego, I cover, and bronchia, gills.) 



