CYCLOBRANCHIAL GASTEROPODS. 
437 
The family of Pterocera, whose remarkable form is so well calcu- 
lated to excite our admiration, has yet another attraction : the colour- 
Rig of the shell exhibits many shades, which are particularly varied 
Fig. 297. Pterocera cliiragra (Linnteus). Fig. 298. Pterocera lambis (Linnaeus). 
Wards the opening, where it is generally distinguished by great 
beshness and brilliancy, which, added to its other characters, render it 
W most interesting of all the Gasteropods. 
Cyclobranchial Gasteropods. 
The Cyclobranchial Gasteropods have the branchix in the form of 
leaflets or small pyramids, attached in one row on each side under the 
e( lge of the mantle. These are essentially marine animals, which form 
Iwo families, viz. Ghitomdm and Paiellidm. 
The Chitons are very singular creatures, destitute of eyes, of 
lentacles, and without jaws ; they hear upon their back in place of a 
Wll a cuirass composed of imbricated and movable scales. They 
have the power of elongating and contracting themselves like the 
flails. They roll themselves up into a ball like the woodlouse. 
They adhere with great force to the rocks, affecting those places most 
