ISCHNOCHITONID^E. 253 



valve having the mucro projecting beyond the narrow eaves ; inser- 

 tion plate obsolete, reduced to a callous ridge, flattened behind, 

 rounded at the sides, and pectinated outside where it joins the 

 sutural plates. 



Girdle fleshy, bearing numerous wide, short, blunt, striated, sepa- 

 rated scales (fig. 29, a young specimen) ; the interstices between the 

 scales covered with a velvety pile. 



Length 75-80, breadth 35-40 mill. 



Peru (Capt. Ridgeley) ; Coquimbo Bay . (Frembly) ; Valparaiso 

 (U. S. Expl. Exped.) 



Chiton niger BARNES, Amer. Journ. of Science and Arts, vii, p. 

 71, t. 3, f. 3 (1824). Enoplochiton niger GRAY, P. Z. S. 1847, p. 69. 

 Chiton coquimbensis FREMB., Zool. Journ. iii, p. 197, t. 16, f. 2 

 (1827). SOWERBY, Voy. 'Blossom' Zool., p. 149, t. 40, f. 6. 

 REEVE, Conch. Icon., f. 22. 



The entire substance of the valves is colored in this remarkable 

 species. Specimens as well preserved as the individual figured are 

 not common ; but so peculiar is the entire shell that it may readily 

 be recognized, however eroded. 



This species like Acanthopleura spinifera, lives upon the rocks 

 between tides in situations exposed to the full force of the surf. In 

 fig. 27 a portion of the surface of a valve is drawn magnified, show- 

 two eyes, megalsesthetes and micrsesthetes ; fig. 28 represents a por- 

 tion more highly magnified, showing two megalsesthetes and the 

 accompanying micrsesthetes. 



Family ISCHNOCHITONIDJE. 



A number of genera belonging to the Ischnochitonidce, were 

 omitted by me in my treatment of it in parts 1 and 2 of this volume, 

 in deference to the views of Carpenter, who grouped them with 

 Acanthopleura and its allies. A more profound study of this and 

 related families, enables me now to see traits of relationship unknown 

 at the time the synopsis on pages 23, 24, 25 was prepared, and there- 

 fore to group the genera more naturally than was then possible. 



Subfamilies of Ischnochitonidce. 



CALLISTOPLACIN.E, in which the slits of the anterior and inter- 

 mediate valves correspond in position to radiating ribs on the exte- 

 rior. (See p. 259.) 



