

FREFA.CE. 



The present volume contains a monograph of the importair 

 extensive Order Polyplacophora, commonly known an Chiton*. 

 Although represented by many species in all seas, tin Chitons have 

 l>een much neglected by Conchologists. This may !>< due to the 

 fact that their characters are not generally understood, or even seen 

 in ordinary cabinet specimens; and again, no illustrated \\<>rk treat- 

 ing the group scientifically has hitherto been produced. Certain it 

 is, that if the serious study of this group be once begun, its at: 

 tious will be found to equal or excel those of any other fain; 

 The numberless modifications of form, the beautiful adapt 

 structure to life-habits and station, the marvelous parallel develop- 

 ments, producing almost identical structures in totally diverse 

 phyla, all distinguish the Polyplacophora as preeminently int< 

 ing among mollusks. 



The author begs those who may use this work to begin by taking 

 apart one specimen of each species to be studied ; then find the genus 

 by the Key on page xxviii. After a certain amount of practice the 

 genus may be ascertained by removing valves vii and viii only ; but 

 guessing it from the external features is in most cases uncertain 

 and unscientific. As a rule, Chitons tell no secrets to those who 

 will not take the trouble to disarticulate them. 



It is hoped that describers of new species will hereafter state the 

 generic characters of their novelties. It is as rational to describe a 

 bivalve without examining its hinge-teeth, as to notice the outside 

 only of a Chiton. 



The synonymy is believed to be practically exhaustive, ex 

 that useless references to mere lists giving no new information are 

 omitted. 



Attention should here be directed to the new theories of the origin 

 of important structures of shell and girdle, given on pp. i\, \ii ; to 

 the original system of classification (p. xxiii), and the phylogenies 

 (pp. xxvii, xxviii). 



The new species described herein which are credited to Car/ 

 rest upon his types when the descriptions are g H* Mt. (as 



in the case of Callochiton princeps, p. 50). In cases where I have 



