CHITONS. 219 



Liimseus assigned the genus to a place among Lepades, 

 but Aclanson transferred it to the immediate vicinity of the 

 VatellcB, and his opinion is confirmed by Cuvier. 



The shell of Chiton, when compared with that of Fa- 

 tella, is not so different as to prevent the expectation 

 of some resemblance in their molluscous inhabitants; it 

 difi'ers^ however, very remarkably in being secreted in 

 eight separate pieces, sustained in order by a horny ex- 

 pansion of the mantle, and moving upon each other, after 

 the manner of plate armour, by the aid of three flexible 

 muscles attaching cross-wise to each plate or valve. The 

 horny expansion of the mantle is sometimes only marginal, 

 constituting a frame to the shell, and is characterized by a 

 variety of ornament. Thus_, in one the horny ligament 

 appears in its simplest form, thin and transparent; in 

 another, it is covered with a rough arenaceous surface ; in 

 another, with thickly-set calcareous bristles. The C.fasci- 

 cularis presents a row of dense tufts of brittle glassy spi- 

 culse ; and in the great C. Sitkeiisis, in which the mantle 

 entirely envelopes the shell, the surface is crowded with very 

 close-set minute stars of glassy spicula3. 



The exposed portion of each valve in the shell of 

 Chiton^ and that which is alone adorned by sculpture or 



