XIV POLYPLACOPHORA. 



of the missing valve. The absence of a valve produces no striking 

 change in the general appearance of the animal, and it would be 

 easy to pass one by among a quantity. These considerations incline 

 me to think that abnormalities in the valves may be less rare than 

 supposed. 



Injuries to the girdle often produce more or less irregular growth. 

 In species having large girdle-scales, such as Chiton s. sir., or the 

 large-scaled Ischnochitons, the loss of scales is repaired by the 

 growth over the injured area of scales much smaller in size, giving 

 it a singularly patched appearance. 



COLLECTION AND PRESERVATION OF CHITONS. 



Chitons may be looked for on all but sandy coasts ; on these they 

 are very rare. Some species, like Nuttallina, Enoplochiton, Acantho- 

 pleura, etc., are found upon the exposed rocks at or near high tide ; 

 others like most Ischnochitons, live under stones between tides or at 

 lowest water ; but it is only by the use of the dredge that any 

 approach to a full representation of the Chiton fauna of any locality 

 can be obtained. No elaborate dredging outfit is required, how- 

 ever, for over nine-tenths of the species being vegetable eaters, live 

 in the littoral (including the laminarian and coralline) zone, and 

 may generally be taken in 25 fms. or less depth ; although num- 

 bers of species extend their range to or beyond the 100 fm. line, and 

 a few (the genera Lepidopleuru* and Hanleya only) live in the cold 

 and dark abyssal region. 



A blunt knife is useful to the collector in detaching Chitons from 

 the rocks etc. ; and the specimens before they have time to curl 

 themselves up, should be placed flat on a narrow strip of smooth 

 wood like a ruler or lath well wetted with salt water, and bound 

 down by winding with soft twine or candle-wicking. This will keep 

 them in a natural position until the tissues are relaxed, when they 

 may be placed in alcohol, or cleaned by cutting away the foot and 

 viscera. If this precaution is not taken they are apt to curl up in a 

 shape which renders them almost useless for dissection or for cab- 

 inet specimens, for they will break rather than flatten out. A large 

 number maybe thus set on a single stick. If they curl up before 

 they can be set, it is best to put thenr in a pan of salt water, where 

 they will eventually straighten out, if alive. 



HISTORICAL NOTES ON THE LITERATURE OF CHITONS. 

 Very few species of Chitons were known to writers upon shells 



