XIV 



POLYPLACOPHORA 



403 



A description has already been given of the dorsal eyes in 



Chiton (p. 187), the nervous system (p. 202), the branchiae (p. 



154), the radiila (p. 228), and the generative system (p. 126). 



The recent Chitons are thus classified by Dr. W. H. Dall : — 



Section I. Chitones Regulares. — Anterior mid posterior 



valves of similar character. 



A. Leptoidea. — Insertion plates obsolete, or, if present, 



unslit ; Leptochiton^ Hanleyia., Hemiartliriim^ Microplax. 



B. IscJinoidea. — Insertion plates sharp, smooth, fissured; 



with eaves ; Tracliydermon.^ Callochiton^ Toyiicella., Schizo- 

 plax^ Leptoplax^ Cliaetopleura^ Spongio chiton^ IscTinochi- 

 ton^ C alii sto chiton. 



C. Lophyroidea. — Insertion plates broad, pectinated, project- 



FiG. 264. — Girdles of 

 various Chitonidae. 

 A, Radsia sulcata 

 Wood, X 2 ; B, 

 Maugeria granu- 

 lata Gmel., x 3 ; 

 CyEnoplo chiton 

 niger Barnes, x 3 ; 

 D, Acantho chiton 

 fascicularis L., x 

 4 ; E, Tonicia fas- 

 tigiata Sowb., x 4. 



ing backward ; Chiton, Tonicia, Eudoxochiton, Oraspedo- 

 chiton. 



D. Acanthoidea. — Insertion plates thrown forward ; Sclero- 



chiton, Acanthopleura, Dinoplax, Midde7idorffia, Nuttal- 

 Una, Arthuria, Phacellopleiira. 

 Section II. Chitones Irregulares. — Posterior valve 

 abnormal, or with a sinus behind. 



E. Schizoidea. — Posterior valve fissured; Lorica, Schizochiton. 



F. Placiphoroidea. — Posterior valve unslit, internally ridged, 



umbo nearly terminal ; Enoplochiton, Ornithochiton, 

 Plaxiphora. 



G. Mopaloidea. — Posterior valve with posterior sinus and 



one slit on each side ; Mopalia, Katherina, Acanthochi- 

 ton, Notoplax. 



