Vol. IX] BERRY— NOTES ON WEST AMERICAN CHITONS 21 



tocostatus Pilsbry, but differs in 1) the lower and more 

 regular radial ribs of the anterior valve; 2) the much more 

 numerous ribs and finer reticulation of the central areas; 

 3) the more strongly carinate ridge; 4) the two rows of 

 easily abraded pustules on each rib of the lateral areas; 

 5) the fine granulation of the lateral areas, and 6) the 

 posterior area of the tail valve being finely granular, perhaps 

 sometimes with small pustules like those of the lateral areas, 

 but not distinctly ribbed. 



The specific name chosen has reference to the fragile 

 nature of the valves and girdle. 



Note : Owing to an unlooked for delay in the publication 

 of the foregoing paper, and the necessity of using the names 

 in another connection, certain of the taxonomic terms origi- 

 nally intended to be used for the first time here have already 

 been briefly characterized in Lorquinia, v. 2, pp. 44-47, 

 January 6, 1919. This reference should therefore be added 

 to the preceding bibliographies of relevant literature.) 



All of the illustrations in the accompanying plates are from 

 photographs by John Howard Paine. 



