AMICULA. 45 



The locality given by Sowerby for Ch. vestitus is " Arctic Ocean " ; 

 but from our knowledge of Beechey's voyage it must have been 

 collected on the American shore, north or north-east of Bering 

 Strait. 



Var. ALTIOR Carpenter. 



Shell similar to emersonii, but nmch longer, narrower, higher; the 

 exposed part larger in proportion to the size of the valves, and wider, 

 trilobate on the central valves and conspicuously rugose-granulate, 

 hardly lirate around the margins. Inside normal ; posterior valve 

 unknown ; central valves with 1, anterior 8 short slits, with 

 delicate grooves extending to the eaves. 



Length of a central valve 7i, breadth 3f mill.; divergence 90°. 

 (Cpr.) 



Pleistocene Drift, Loiver Canada (Mus. Dawson.) 



Only one anterior and two central valves have been found of this. 

 On a careful comparison with the corresponding valves of the living 

 species, it appears that the shape more resembles Oryptoconchus ; 

 that the exposed part was nearly as large (in the head valve 

 decidedly larger) as in a specimen of emersonii nearly double its 

 breadth, and that the ribbed frame-work of the shield was Avanting. 

 ( Cpr.) 



A. PALLASii Middendorff. PL 5, figs. 1-11. 



Shell nearly concealed by the girdle, a somewhat heart-shaped 

 tegmentum only being visible at the apex of each valve; elevated 

 at an angle of 98°-110° in the young, 120° in large adults; oval, 

 elongated. Valves white, smooth, fragile, the tegmentum cordiform, 

 posterior. Slits in anterior valve 6-8, posterior valve 2. 



Girdle roundly covering the entire back of the animal, except for 

 8 small rounded holes along the median line ; color dingy buff; dorsal 

 surface bearing all over unequal bunches of reddish hairs, appearing 

 to be sparser in the young. Branchiae extending forward two-thirds 

 the length of the foot. 



Length 67, breadth 48, alt. 21 mill. 



Okhoiosk Sea (Midd.) ; Prihiloff, Aleutian and Shwnagin Is. 

 (Dall). in 3-lOfms. 



Chiton pallasii Midd., Bull, de la Classe physico-mathem. de 

 I'Acad. de St. Petersb., vi, p. 117 (1847).— (7/iito?i (Phcenochiton, 

 Dichachiton, Symmeirogepliyrus) pallasii Midd., in Middendorff's 

 Reise in den iiussersten norden und osten Siberiens, ii, Zool. pt. 1, p. 



