28 < II.V.KTI.Kt i: \. 



.Jouni. v, p. 28, represented by Chiton spin osus 8by, The 



Indian -pecies belongini: to this section (A. picea) must have 

 been familiar to him and u'iven ri>e to the " /<ma crassa carnosa" 

 of h;> diairno>i>. with which < 'iKctoj.leura does not accord. The 

 -ntcd lv < '. peruvianus 1'onns only tlie sixtli among 

 seven sections into which Guilding divided his genus. 



Bhottleworth and Adams place the hairy chitons, in Chsetopleura 



and those with shelly l>ristle> in Acanthopleiira. 



The distinction is obvious as between peruviana and picea, but 

 not so in t lie cast' of many -pecies \\lien the bristles are corneous but 

 With more or len of shelly matter in their substance. There are 

 also ma; | in which the hairs are shortened and flattened 



into chaffy scales and others in which hairs grow irregularly in the 

 midst of a spongy or chaffy mass. Gray, moreover, assigns "shelly 

 t- the peruviana group and " shelly spines or bristles " to 

 tin- picea jrroup. Tothefir-t. however, are assigned thin, to the 

 second thick valves. Both are described as having the insertion 

 plate- pectinated ; but as being " regular well developed " in peru- 

 viana, hut "narrow, rather irregular " in picea. This last results 

 from what seem- to me the essential difference. Acanthopleiira is 

 hunch-hacked on the tail plate, with the insertion plates thrown for- 

 ; and L'r-'ovcil outside ; while Chretopleura has the normal tail 

 plate of Chiton and Ischnochiton and agrees with the latter genus 

 in having the insertion plates not pectinated and nearly smooth. 

 The transition forms from the densely pilose peruviana to the 

 smooth mantle of Tonicella are so gradual that the latter might 

 rank as a subgenus under Chsetopleura were it not that the gills in 

 tin- ircmis are represented as elongate. (Cpr.) 



< 'h;etopleura should be compared with the Lophyroid genus Ton- 

 icia, which has similar ambient gills and solid eaves, and frequently 

 has th- t--r i h scarcely more pectinated than in the larger Chieto- 

 plcuras. 



The genus consists of several groups of species. (1) Typical 

 ;h-r large, and having very delicate sculpture; and (2) 

 Group of C.gemmea, having the lateral areas strongly raised and 

 coarsely sculptured, the central areas also sculptured. 



(1). Urniij, of C. 



n \I\N\ Lamarck, IM. rj, ii^. 42-46. 



ssed, dull a.-h colored, the girdle clothed with 

 long, Stifi*. crUp black hair, a fringe of which also projects from each 



