XXIV PO.LYPLACOPHORA. 



toward greater definiteness in the positions of the slits, and often 

 nl the degeneration of the >h -11 ; leading (a) through Callisto- 

 placiiuf to the Mopnliidn, and (6) through Acanthochitidce to covered 

 forms, Cryptochiton, and to worm-like forms, Cryptoplacida* ; the 

 last having fewer slits than any other Chitons. In the other direc- 

 tion (II) the slits became generally more numerous, the insertion- 

 plates are roughened for the stronger adhesion of the girdle, the 

 valves increase in general effectiveness as a protective armor, and 

 thrir sense organs became highly developed. This phylum (Chi- 

 nlminates in / vthoplewra, Schizochiton, Enoplo- 



chiton, Liolophnra, etc. ; and may be regarded as the highest group 

 of Polyj'hu'ophora. 



NOTK. It must be understood that in cases where the classifica- 

 tion below given differs from that in the descriptive part of this 

 work, the former represents the mature views of the author. Page 

 n the text, should be cancelled, as it was written when but a 

 small portion of the groups there discussed had been studied. The 

 synopses given on pp. 24-25, and 148-149 also require correction. 



pris of Classification of the Order Poly placophora. 

 I. Superfamily EOPLACOPHORA. 

 Family Lepidopleiiridce Pilsbry. 

 nus Lepidopleurus Risso. p. 2. 



Section Deshayesiella Cpr., p. 16. 

 Genus Hanleya Gray, p. 17. 

 * 



Genus Hcrniai thrum Cpr., p. 19. 

 * 



Genus Microplax Ad. <fe Ang., p. 21. 



1 1 Superfamily MESOPLACOPHORA. 

 Family l*cl<n<>chttn lt i<l<i Pilsbry, p. 253. 

 Subfamily Ischnochitoninse Pilsbry, p. 254. 

 Genus Tonicella ( j.r , p. 40. 

 nis Schizoplax Dall, p. 46. 

 usCallochiton (iray, p. 48. 

 Section Sterochiton Cpr., p. 52. 

 Genus Trachydermon Cpr. p. 67. 



