186 SYSTEMATIC ARRANGEMENT 



spicula ; valves entirely hidden, consisting wholly of the plate of 

 insertion ; anterior valve divided into five pectinated lobes. Gills 

 extending the whole length of the side. 



1. C. amiculatus. 



2. C. Stelleri, Middend. Mai. Ross. t. 1. f. 1, 2 ; Adams, Gen. Moll. 



t. 55. f. 1. 



Central teeth of Cryptochiton Stelleri (see Middend. Malac. Boss. 

 i. 141. t. 3. f. 10, 11, 12, t. 5. f. 9) small, squarish; iDner lateral 

 elongate, erect, curved, linear, three-toothed at the tip ; the others 

 flat, four-sided, elongate ; inner smaller, gradually larger towards 

 the outer series, which are largest, transverse, obscurely toothed 

 on the front edge. 



B. The mantle with nine pores on each side, the two front on the 

 front margin of the anterior valves, and each of the others 

 at the hinder edge of the side of each valve, all furnished with a 

 tuft of spicula or bristles. 



a. Mantle bald, spinulose beneath, the pores of the mantle fur- 

 nished with subulate flexible bristles ; the exposed part of the 

 valves broad. 



18. Plaxiphora. 



Mantle with scattered tufts of bristles, and with a series of nine 

 tufts of larger bristles on each side ; valves broad, exposed, thin ; 

 the plate of insertion of anterior valve lobed, of middle valve with a 

 notch on each side, of the hinder valve entire, smooth, rounded ; the 

 hinder valves with a produced subposterior apex. 



1 . PI. Carmichaeli — Chiton albidus, Ch. raripilosus, Ch. costatus, 

 Blainv., Ch. biramosus, Quoy, Ch. setiger, Ch. Fremblii, and 

 Ch. setosus, Sow. Terra del Fuego. 



b. Mantle spinulose, with the pores furnished with tufts of bristle- 

 like calcareous spines ; exposed part of valves moderately large. 



19. Hanleya. 



Body depressed. Mantle spinulose ; lateral tufts of spines small ; 

 exposed part of valve broader than long ; margin of insertion of the 

 valves entire, of anterior and posterior valves very narrow. 



1. H. debilis = Chiton Hanleyi, Thorpe. 



20. ACANTHOCHETES. 



Body oblong elongate, rather depressed. Mantle spinulose, tuft 

 of spines generally large, often iridescent ; exposed part of valves 

 moderately broad cordate, as long as broad. Gills occupying two- 

 thirds of the hinder part of the sides of the foot. 



