346 CHITONID^. 



H. Gryptoidea. 



With double sutural laminae. 



CRYPTOCONCHUS, Guilding. Insertion-plates regular, variable 

 behind ; anterior valve with five slits, middle one, posterior irreg- 

 ular; teeth very long, smooth ; eaves minute ; sinus deep, arched ; 

 girdle smooth, tufted; valves nearly covered ; gills one-third. G. 

 porosus. 



AMicuLA, Gray. (Symmetrogephyrus, Midd. Stimpsoniella, 

 Cpr.) Shell regular; exposed valves small, mucronate or sub- 

 cordate ; posterior sutural laminae large ; girdle more or less 

 pilose, sometimes poriferous. Branchise median in the typical 

 group. G. Pallasii, Midd. (Ixxxvi, 92). 



CHLAMYDOCHiTON, Dall. Brauchise encircling. The Amiculse 

 are provided with pores bearing fasciculi of bristles of a soft or 

 horny character, and which, while often irregularly disposed or 

 even almost entirelj^ absent (in particular individuals), have a 

 tendency to arrange themselves in two rows on each side of the 

 median line, one row behind the exposed point of the valve, and 

 another near its submerged lateral posterior angle, on each side. 

 The mantle is also provided with a coating of fine, chaffy, decid- 

 uous scales. G. amiculatus, Pallas (Ixxxvi, 93). 



GRYPTOCHiTON, Midd. and Gray. Yalves entirely immersed in 

 the girdle, which is minutely fasciculately pilose. Branchiae 

 encircling. G. Stelleri^ Midd. (Ixxxv, 83) is the largest of the 

 Chitons, attaining a length of eight inches. The valves are 

 entirel}^ covered, so that their outline even is not indicated in 

 fresh specimens, although plainly marked in those which have 

 been dried. The Aleutians and Indians eat the foot and softer 

 parts, in the raw state. 



I. Ghitonelloidea. 

 Tail-plate funnel-shaped, laminse thrown forward. 



Chitonellus, Blainville. 



Insertion-plates very sagittate; slits in anterior valve 5, in 

 middle 0-1, in posterior none ; teeth very short, except at sutures ; 

 eaves distinct ; sinus A^ery deep and narrow ; girdle crowded with 

 bristles, no tufts ; gills posterior. The species enjoy considerable 

 powers of locomotion compared with other groups of the family. 

 G. faaciatas, Quoy (Ixxxv, 95). 



CRYPTOPLAx, Gray. Middle valve without slits ; girdle with 

 crowded bristles, tufted. 



CHONEPLAX, Cpr. Animal creeping, rather long; exposed 

 valves small, contiguous ; last one infundibuliform ; mucro 

 recurved, terminal ; laminae as in Katherina, but obsoletely slit; 

 girdle as in Acanthochiton. G. striatus, Sowb. (Ixxxv, 84). 



CHiTONisus, Cpr. Girdle not poriferous. Based on G. striatus 



