28 CH^ETOPLEURA. 



Zool. Journ. v, p. 28, represented by Chiton spinosus Sby. The 

 West Indian species belonging to this section (A. picea) must have 

 been familiar to him and given rise to the " zona crassa carnosa " 

 of his diagnosis, with which Chsetopleura does not accord. The 

 latter as represented by C. peruvianus, forms only the sixth among 

 seven subgeneric sections into which Guilding divided his genus. 

 Shuttleworth and Adams place the hairy Chitons in Chsetopleura 

 and those with shelly bristles in Acanthopleura. 



The distinction is obvious as between peruviana and picea, but 

 not so in the case of many species when the bristles are corneous but 

 with more or less of shelly matter in their substance. There are 

 also many species 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 

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

 the picea group. To the first, however, are assigned thin, to the 

 second thick valves. Both are described as having the insertion 

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

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

 from what seems to me the essential difference. Acanthopleura is 

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

 ward and grooved outside ; while Chsetopleura 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 

 this genus are represented as elongate. (Qor.) 



Chsetopleura should be compared with the Lophyroid genus Ton- 

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

 has the teeth scarcely more pectinated than in the larger Chseto- 

 pleuras. 



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

 forms, rather 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). Group of C. peruviana. 



C. PERUVIANA Lamarck. PI. 12, figs. 42-46. 



Shell oval, depressed, dull ash colored, the girdle clothed with 

 long, stiff, crisp black hair, a fringe of which also projects from each 



