CHAPTER XVI. 
PROSOBRANCHIATE GASTEROPODS. 
In the Prosobranchiate division of the Gasteropods the branchiz or 
gills are composed of numerous leaflets cut like the teeth of a comb, 
and attached, by one or many lines, to the upper part of the respiratory 
cavity. They constitute the most numerous order of Cephalous 
Molluscs, comprehending nearly all the univalve spiral shells, and 
many others which are simply conical. They inhabit the sea, rivers, 
and lakes, and are of all sizes. The most remarkable genera which 
we shall describe belong to the family Zrochoide and Buccinoide. 
This, the fourth order of Gasteropods, Prosobranchiata, includes 
the Pectinibranchiata and three other orders of Cuvier; in it the sexes 
are distinct, the branchiz pectinated or plume-like, situated (Jroso) in 
advance of the heart, 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, o/ostomata, contains the sea-snails, where 
the margin of the aperture of the shell is entire. The muzzle is short, 
non-retractile, and they are mostly phytophagous. The second section 
contains the carnivorous Gasteropods. The aperture of the shell is 
notched or produced in front; animals with a retractile proboscis. 
Unlike the first section, the species are all marine. 
The first family is that of the Chztonide, The Chitons are very 
singular creatures, destitute of eyes and of tentacles ; 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 roll 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 magnificus 
(Fig. 210) is widely distributed. 
The second family, Dentaliade, supplies the curious genus 
Dentalium, or tooth shell. 
The Patellida, or Limpets, constitute the third and a very 
numerous family, distinguished at once by the form and structure of 
