96 Descriptions of British Chitones and other shells, 



possible, and the more obvious characters, when sufficient, ought 

 always to be preferred. There is something also of an artificial 

 nature in this character, which has determined me to consider it 

 as subordinate to those I have just mentioned ; and to exclude it 

 from the specific phrase, though not absolutely from specific des- 

 cription. In some instances, indeed, it will be found of the 

 greatest use in confirming distinctions which might otherwise ap- 

 pear mere accidental modifications. 



All characters founded on colour have been rejected, as obvi- 

 ously uncertain ; though even in this there is a peculiarity of habit 

 observable in most individuals of a species. Differences in shape, 

 in shells like these, so much allied in general outline, are ex- 

 tremely difficult to define, and will not I fear be found to afiford 

 sufficiently striking peculiarities for specific character. 



The fringe, which by some writers has been relied on with so 

 much confidence in the description of Chiton cinereus^ is, with 

 different modifications, common to all the species ; though it is cer- 

 tainly much more conspicuous in that than in any of the others, 

 with the exception perhaps of C» fascicular is. 



I have not yet been fortunate enough to meet with any Chito- 

 nes having fewer than eight valves ; but I should imagine there 

 can be little hesitation in considering all such as mere accidental 

 varieties. 



* LIGAMENTO MARGINIS SPINOSO. 



1. Chiton fascicularis. 



C. testa subcarinata ; valvulis carina longitudinaliter striata, 

 lateribus granulatis ; margine granuloso, subspinoso, rudi, setarum 

 fasciculis utrinque. 



Valvuli medii dentibus 2 utrinque, primo maximo, altero 

 parvo. Valvulus 1""" dentibus 6, latioribus ; ultimus utrinque 

 emarginatus, interstitio fere crenulato, aliquando dentato. 



Icon. Chem. Coch. 10. t. 173. f. 1688.— Encye. Mcth. pi. 163. 

 f. 15.— Adans. Hist. Sen. p. 42. t. 2. f. 11 ? 



removed the ligament, to fasten each valve separately in their proper order 

 on a card, with gum, by their outside, when the teeth may be conveniently 

 observed. 



