ISCHNOCHITON. 71 



Arctic and North Atlantic Seas; Greenland; Iceland; Spitz- 

 bergen; Scandinavia; British Seas, south to Isle of Man; Gulf q 

 St. Lawrence, Maine, and south to Massachusetts Bay (Cape Cod). 

 In the Pacific from Arctic Ocean, south to the Shumagin Is., west to 

 Kyska. Low water to 337 fins. 



Chiton albus LINNE, Syst. Nat. xii, p. 1107. LOWE, Zool. Journ. 

 iii, p. 80. SOWB., Conch. 111. f. 99, 100. GOULD, Inv. Mass. p. 

 150, f. 21. MIDD., Mai. Ross, i, p. 120. FORBES & HANLEY, 

 Brit. Moll, ii, p. 405, t. 62, f. 2. STIMPSON, Sh. of N. Engl. p. 28; 

 Inv. of Grand Manan p. 22. JEFF., Brit. Conch, iii, p. 220 ; v. p. 

 199, t. 56, f. 3. BINNEY, in Gould's Invert. Mass. p. 265, f. 525. 

 ? Chiton oryza SPENGLER, Skrift. Nat. Selsk. iv, hft. 1, 1797, teste 

 Jeffr. Ch. aselloides LOWE, Zool. Journ. ii, p. 103, t. 5, f. 3. 

 WOOD, Index Test., Suppl., t. 1, f. 9. Ch. sagrinatus COUTHOUY, 

 Amer. Journ. Sci. xxxiv, p. 217, 1838; Bost. Journ. ii, p. 82. 

 Leptochiton albus H. & A. AD., Gen. Rec. Moll, i, p. 473. Chiton 

 (Lepidopleurus) albus JEFFREYS Brit. Conch, iii, p. 210. Ch. 

 (Lophyrus*) albus JEFFR. P. Z. S. 1882, p. 669. Lophyrus albus 

 SARS, Moll. Reg. Arct. Norv. p. 114, t. 8, f. 2 (? not t. I, f. 9). 

 ? Ch. minimus GMEL., Syst. Nat. xiii, p. 3205. Trachydermon 

 albus CARPENTER, New Engl. Chitons, Bull. Essex Inst. v. p. 153 ; 

 MS. p. 15. BALL, Proc. U. S. Nat. Mus. 1878, p. 322. 



This well known Arctic and subarctic species is intermediate 

 between Tr. cinereus and Tr. ruber in sculpture. The granulation 

 is much finer than in the former of these, but is on the same general 

 plan. 



On pi. 6, figs. 32-34, is copied a Carpenterian drawing of the 

 interior of Tr. albus. It is, however, incorrect, the form of head 

 and tail valves being unusual, and the slits of the latter entirely 

 incorrect. The central valve is well represented however. The 

 tail valve of a specimen from Grand Manan, drawn by the writer, 

 is shown in fig. 38 of plate 7, correctly delineating the slits. 



I. EXARATUS Sars. PI. 7, figs. 39-49. 



Elongated, oblong-elliptical, strongly convex ; valves distinctly 

 obtusely carinated medially. Anterior valve nearly semicircular 

 in front ; the posterior edge forming an obtuse reentrant angle r 

 with a rounded notch in the middle ; surface distinctly, radially 

 grooved with single rows of rounded granules between the grooves, 

 becoming larger toward the margin. 



