PART II. CYCLOBRANCHIA. 357 



produced and slightly curved inwards ; muscular im- 

 pression semi-circular. 



Hipponyx De Fr. Cap-shaped or patelliform ; strong ; 

 the margins thick, and reposing upon a thin, flat- 

 tened ; testaceous plate, forming a second valve, 

 cornucopia. Sow. Man. f. 199. 



Pileopsis Lam. Shell cap-shaped ; thin ; the apex 

 much produced and incurved ; no basal support or 

 internal appendage. 



P. Hungaricus. Sow. Man. f. 240. 



Pedicularia Sw. Shell irreg-ular, sub-patelliform ; 

 a thick, large, obsolete apex on one of the longest 

 sides, and an internal callous rim within, on one 

 side only ; circumference undulated, irregular. 

 P. Sicula^M?. (fp. 44.) 



Patella Linn. Shell entire, simple, cup-shaped or 

 patelliform ; apex pointed, entire.* 



P. miniata. Sow. Gen. f. 2. 



Siphonm'ia Sow. One side more dilated than the other, 

 and marked by an internal groove. 



S. Sipho. Sow. Gen. f. 1. 



Tribe 4. CYCLOBRANCHIA. The Chitons. \ 



Animal patelliform, oval ; the mantle coriaceous ; the 

 back covered with imbricate shelly plates ; no tentacula. 



Chiton Lin. Back with large transverse plate ; zone, 

 or mantle, wide, covered with small scales, either 

 imbricate or reticulate. 



C. squamosus. Sow. Gen. f. 2. 



Canthapleura Guild. Plates as in Chiton ; the 



* The fresh-water genus Ancylus has the same shaped shell, but the 

 animal shows it belongs to the lAmnniancE. 



t Not having analysed this tribe, I have adopted the genera and arrange- 

 ment of Guilding, see Zool. Joum. xvii. p. 27., especially as they thus form 

 a circular group. 



A A 3 



