TONICIA. 201 



central 1, posterior valve 14 slits ; teeth very sharp, pectinated. 

 Sinus flat moderately deep and broad, with up to 16 teeth. 

 Length 30, breadth 17 mill.; divergence 105. 



T. ATRATA Sowerby. PI. 41, figs. 28, 29, 30. 



Shell oval-oblong, smooth, subcarinated ; valves nearly straight, 

 subrostrate ; lateral areas inconspicuous ; margin [girdle] smooth. 



Length 25, breadth 12* mill. (Swob.) 



The smooth, narrow, slightly angulated species above described is 

 of a blackish-brown color; the lateral areas are not distinctly 

 marked except by rays of lighter color in some specimens on them, 

 and on the terminal valves. (/Sou; 6.) 



Falkland Is. (Sowb.) ; Orange Harbor (U. S. Ex. Exped.) 



Chiton atrata SOWB. in Charlesworth's Magazine of Nat. Hist. 

 1840, p. 294 ; Conch. Illustr., f. 57, 58. REEVE, Conch. Icon., 1. 17, 

 f. 103. GOULD, U. S. Expl. Exped., p. 329, f. 415. Tomcia atrata 

 H. & A. ADS., Gen. Rec. Moll, i, p. 474. ROCHEBRUNE, Polyplac. 

 Cap Horn, p. 138. T. boetica CPR., MS. olim. 



I have not seen this species. Carpenter writes : Mucro more or 

 less elevated, tumid behind. Inside having 8 slits in the anterior, 

 1 in the middle and 12 in the posterior valve; teeth acute, outside 

 and at the edge sulcate, scarcely pectinated ; sinus moderate, flat, 

 with 13-20 denticles. 



Hutton reports this species from Macquarie Island, N. Z., but 

 says : " Our species agrees very well with Reeve's figure, but not 

 with his description. The anterior terminal area is distantly 

 radiately ribbed, and the lateral areas are sometimes defined by a 

 single rib. The umbone of the posterior valve is more posterior 

 than in the drawing, and the valves are of a uniform brown color. 

 The mantle is of the same color as the valves." These characters 

 seem to me to indicate a distinct species, which may be called 

 Tonicia subatrata. 



T. SWAINSONI Sowerby. PL 43, figs. 41, 42. 43, 



Shell oval, moderately or decidedly elevated, somewhat carinated, 

 the side-slopes nearly straight. Ground-color light pinkish-buff, 

 painted all over with a multitude of red or red-brown lines, concentric 

 to the beaks ; often having some valves striped at or on each side of 

 the ridge, or more or less completely covered with dark red-brown. 



Lateral areas little raised, sculptured with about 8 radiating 



