166 



LESLIE B. AREY AND W. J. CROZIER 



kinds and number of these epizoites depend upon the size of the 

 Chiton and the character of its habitat. The most conspicuous 

 of them are barnacles (Tetrachta, fig. 1), Spirorbis, and Serpula. 

 To this group must be added algae, comprising not merely the 

 thin coating upon the valves, but also the Enteromorphas, which 

 (in appropriate habitats) grow plentifully upon and between the 



Jr. 



IZ9.4^ 



8.8, 





^■7c/ns 



IL. 123./ 

 7-7 cms. 



/• f Cfrts. 



(S2) (xl'/z) 



^.'2f.^6 



Fig. 3 Outlines of the fourth valves of five chitons of increasing ages (sizes) ; 

 dorsal aspects, anterior up; see text. X 4. 



Fig. 4 Illustrating protective growth of the valve substance resulting from 

 the presence of epizoic barnacles; the outline is that of the valve. X 1. 



scales of the girdle. They are very important for the production 

 of homochromic effects, because the periostracum of the scales 

 is but little eroded, even in large chitons. The valves are rarely 

 much overgrown with these algae, except among the largest 

 chitons. In the felted matting of algae various j^oung mollusks, 

 nematodes, archiannelida, and protozoa abound. The serpulas 



