36 



C. elegans it appears in its simplest form, thin and transparent; in C. 

 alatus it is covered with a rough sandy deposit, in C. Blainvillei with a 

 few scattered bristles, in C. Peruvianas with a dense growth of hair, in C. 

 seliger with straggling bristle-like hairs, in C. Coquimbensis with oblong 

 beads, in C. aculeatus with short cylindrical spines, in C. spinosus with 

 sharp curved spines, in C. magnificus with close-set calcareous grains, in 

 C. squamosus with close-set scales, in C. fascicular is with tufts of little 

 bristly spiculse, and in C. Sitkensis, in which the mantle entirely covers 

 the valves, with minute stars of glassy spicule. 



The imbedded portion of each valve is more or less produced posteriorly 

 into two processes, according to the oblong tendency of their structure, and 

 the comparative force necessary to keep them in order. In most species 

 where the valves are narrow across, these processes, termed apophyses, from 

 their analogy with the apophysis of the vertebrate skeleton, are but slightly 

 developed, and the sinus between them is finely serried. In valves of a 

 more oblong form, as in C. incisus, the apophyses become more prominent, 

 until in Chitonellus, where the valves are longer than wide, and isolated 

 from each other, the apophyses are developed to an extent that enables the 

 valves to be sustained each by itself in the substance of the mantle. The 

 exposed portion of each valve, the only part that is characterized by any 

 sculpture or design of colouring, has the appearance of a convex shield, 

 supported on either side by a raised, triangular, winged growth, forming, as 

 it were, the radii of a circular plate, which meet together in the anterior 

 terminal valve ; so that the sculpture and colouring of the front valve is 

 almost invariably the same as in the lateral areas of the rest ; and the 

 sculpture and colouring of the central areas of the valves is as invariably 

 different. 



The Chitons live attached to stones and fragments of shells in deep 

 water, sometimes on exposed rocks, but most frequently under stones at 

 about low-water mark. They exist in abundance on the shores of south- 

 western America, of Australia, and New Zealand, the Eastern Archipelago, 

 the Pacific Islands, Cape of Good Hope, West Indies, Sitka, and the 

 shores of Europe and Asia, six species inhabiting our own shores. 



The genus has been subdivided chiefly according to characters of the 

 encircling cuticle. 



Species. 



1. aculeatus, Linn. 6. alatus, Sow. 11. arbutum, Reeve. 



2. acutiliratus, Reeve. 7. albilineatus, id. 12. articulatus, Sow. 



3. acutirostratus, Ad. Rve. 8. amiculatus, Pallas. 13. assimilis, Reeve. 



4. Adelaidensis, Reeve. '.). antiquus, Reeve. 14. astriger, id. 

 a. aereus, id. 10. aquatilis, id. 15. atratus, Sow. 



