ONITHOCHITON. 249 



Chiton quercinus GLD., Proc. Bost. Soc. Nat. Hist, ii, p. 142 

 (1846); U. S. Expl. Exped. Moll., p. 312, f. 437, 437a; Otia 

 Conch., p. 3. C. (Onithochiton) quercinus GLD., Otia, p. 242. 



Closely allied to 0. lyelli and 0. rugulosus. 

 O. RUGULOSUS Angas. PL 55, fig. 19. 



Shell elongately ovate, a little narrowed in front, raised and car- 

 inated, pale yellowish-brown, the central areas of the valves faintly 

 spotted with olive, the outer edges bordered with green, upon which 

 and extending inward are concentric waved bands of olive brown 

 darker at the margin; lateral areas not raised, divided from the 

 dorsal areas by radiating nodulous ribs, transversely rugosely, costate ; 

 dorsal areas finely longitudinally ridged ; mantle brown, variegated 

 with ash-color and clothed with very minute chaff-like scales- 

 (Ang.) Length 16 mill. 



Port Jackson, Australia. 



OnithocUton rugulosus ANG., P. Z. S. 1867, p. 115, 223, t. 13, 

 f. 29. 



Carpenter gives the following notes upon the type specimen : 

 Shell broad, the valves much beaked, dorsal ridge acute. Mucro 

 terminal. Jugal area scarcely distinct, smoothish ; central areas 

 having about 16 nearly longitudinal, jagged wrinkles, nearly meet- 

 ing over the jugum. Lateral areas very sharply rugose, much 

 more so than in the other species, the rugae about 12, not developed 

 in young shells, very irregular, swelling into granules especially on 

 the diagonal lines and sutures. Anterior valve having 8 lines of 

 black dots, with two additional, indistinct ones. Inside whitish with 

 a brown spot in the cavity ; posterior valve having the mucro 

 absolutely terminal, the insertion-plate planed off. Anterior valve 

 having 8 slits ; teeth very finely rugose ; sinus deep, flat, tolerably 

 broad, with about 20 fine teeth. Girdle covered with minute hairs. 



Length 16i, breadth 12 mill.; divergence 125. 



O. AMICORUM Baird. PI. 54, fig. 46. 



Shell rather elongated, elevated, with acute dorsal ridge. There 

 is a line of reddish-brown color along the dorsal ridge, and one or 

 two others along the sides. 



Lateral areas much elevated, with very nodulous wrinkles, two or 

 three irregularly concentric ; these are partly on the diagonal and 

 sutural ribs, with others intercalated. Central areas with about 22 

 slightly irregular riblets, nearly longitudinal, but bending toward the 



