322 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



what produced behind into two corners. The eggs in part of the ovisac 

 were well developed, and resembled the figure of the youngest stage 

 given by Loven. Anus median, inconspicuous, close to the mantle-edge. 

 On each side of it, midway between it and the posterior ends of the gill- 

 rows, is a fold containing the ovarian fenestra?. The number of openings 

 varies from three to six in different individuals. They are linear, oblique, 

 and close together. They are more strongly marked in this species than 

 in any other Chiton I have examined. 



Trachydermoa albus. 



Chiton albus Lin. S. N. ed. xii, p. 1107, No. 8, 1766. — Lowe, Zool. Journ. iii, p. 80, 

 1826.— Fabricius, Faun. Gronl. p. 422, 1780.— Sowerby, Conch. 111. Chiton, t 

 99, 100, 1839.— Gould, Iuv. Mass. p. 150, f. 21, 1841.— Loven, Ind. Moll. Lit. 

 Scand. p. 27, 1846.— Middendorf, Mai. Ross, i, p. 120, 1847.— Forbes & Han- 

 ley, Brit. Moll, ii, p. 405, pi. lxii, f. 2, 1853.— Hanley, Shells of Lin. p. 17, 

 1855. — Stinipson, Sh. of New Eugl. p. 28, 1851 ; lb. Mar. Iuv. Grand Manau, 

 p. 22, 1853.— Jeffreys, British Conch, iii, p. 220, 1865 ; v, p. 199, pi. lvi, f. 3, 

 1869.— Binney's Gould, p. 263, f. 525, 1870. 



? Chiton oryza Spengler, Skrift. Nat. Selsk. Bd. iv, Hft, 1. 1797 (fide Jeffreys). 



Chiton aselloides Lowe, Zool. Journ. ii, p. 103, t. 5, f. 3, 1825. — Wood, Ind. Test. 

 Suppl.pl.l,f.9, 1828. 



Chiton sagrinatus Couthouy, Am. Journ. Sci. xxxiv, p. 217, 1838; lb. Bost. 

 Journ. Nat. Hist, ii, p. 82, 1838. 



Leptochiion albus H. & A. Adams, Gen. Rec. Moll, i, p. 473, 1854. 



C. (Lepidopleurus) albus Jeffreys, Brit. Conch, iii, p. 210, 1865. 



Tracliydermon albus Carpenter, New Engl. Chitons, Bull. Essex Inst, v, p. 153, 

 1873. 



C. {Lcptochiton) albus Morch, Moll. Greenl. 147, 1875. 



Lophyrus albus G. O. Sars, Moll. Reg. Arc. Norv. p. 114, t. 8, f. 2 a-b (probably 



not t. I, f. 9 a-b), June, 1878. 

 t Lophyrus exaratus G. O. Sars, 1. c. p. 113, t. 8, f. 1 a-k, t. ii, f. 1 (bad). 

 t C. minimus Gmel. S. N. p. 3205, 1788. (Bergen. ) 



Tr. t. mucrone mediano, parum elevato ; intus, v. post. 10-, ant. 13-, 

 centr. 1-fiss. ; dent, acutissimis, posticis interdum serratis ; subgrundis 

 spongiosis; sinu modico, undulato, hand angulato, hevi; zona squamu- 

 lis solidioribus ; branchiis medianis. Lon. 10, Lat. 5-G mm. Di v. variable. 



Hab. — Arctic and boreal seas, Atlantic and Pacific. British seas 

 south to the Isle of Man ; Scandinavian seas, 10 to 100 fathoms (as ex- 

 aratus to 200 fathoms) 5 Spitzbergen; Iceland; Greenland, White Sea; 

 Gulf of St. Lawrence; Massachusetts Bay; on the Pacific from the 

 Arctic Ocean south to the Shumagins and west to Kyska and probably 

 to Attn, low water to 80 fathoms, on stones and shells. Two hundred 

 and forty-eight specimens examined. 



The synonymy of this species might have been much enlarged under 

 the old name of Chiton albus, but to no particular purpose. It is a well- 

 known and characteristic Arctic shell. American and particularly deep- 

 water Alaskan specimens are larger, finer, and better display the scales 

 of the girdle than European specimens. Sars' exaratus would seem to 

 be probably of this description. 



It seems also to be more common to the westward. Its chief pecu- 



