PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 321 



Trachydermon ruber. 



Chiton i)itniceus Coutliouy (MS.)« — GIA. Otia Conch, p. 5, 1846 (probably). 

 Leptochiton ruber H. & A. Adams, Geu. Eec. Moll, i, p. 473, 1854. 

 Chiton {Lciiidopleurus) ruber Jo^&eys, Brit. Moll, lii, p. 210, 1865. 

 Trachydermon ruber Carpenter, Bull. Esses Inst, x, p. 153, 1873. 

 Boreochiton ruher G. O. Sars, Moll. Eeg. Arc. Norv. p. 116, t. 8, f. 4 a-1, t. II, f. 

 3 a-c (imj)erfect), June, 1878. 



Tr. t. mucrone mediaiio, satis elevator intus, r. post. 9-11-, ant. 8-11-, 

 centr. 1-flss. lajvi; dent, interdiim solidioribus, interdum i)ostice rugii- 

 losis; subgrimdis modicis; siiin lato, i)lanato; zona normali; branchiis 

 submedianis. Lou. 25, Lat. 8 mm. 



Hab. — Northern seas, widely distributed; whole coast of Norway, low 

 water to 40 f. (Sars); Arctic and northern seas of Europe; Adriatic? 

 (Olivi!) ; Spitzbergen, Iceland and Greenland, Ne^ England, Gulf of St. 

 Lawrence and Labrador coasts ; Tartary (Lischke) ; Kamchatka ; and in 

 Alaska from the Pribiloff Islands westward to Attn and southward to 

 Sitka, low water to 80 fathoms, on stones and shells; probably also to 

 Bering Strait northward. Two hundred specimens examined. ? Orange 

 Harbor, Patagonia, as C. piiniceus. 



This shell is apparently smooth, as described by Forbes and Hanley, 

 but under a high j)ower appears finely reticulated, as observed by Jef- 

 freys. Its color is very variable, being usually marbled red and whitish, 

 like Tonicella marmorea, but the valves may be uniform dark red or nearly 

 imre white. I have one specimen with the four central valves dark red 

 and the rest white; one valve in a specimen is often dark red, while all 

 the others are marbled. It is most likely to be confounded with Toni- 

 cella marmorea and some varieties of T. Jineata, both of which have 

 leathery girdles, while this species can almost always be determined by 

 its farinaceous girdle, dusted with alternate red and whitish patches, the 

 latter nearly opiiosite the sutures. 



The identity or locahty of Dr. Gould's specimen, described as G. puni- 

 ceus Couthouy, and supposed by Dr. Carpenter to be probably the same 

 as our northern species, seems questionable. 



This species has been much confused by European authors, who have 

 persisted in referring the Linuean name to T. marmorea Fabr., and resur- 

 recting the indeterminate figure of Pennant for this species, though Mr. 

 Hanley has determined the identity of the Linnean specimen with this 

 species, and he did not possess the marm o rea. The synonymy here quoted 

 is only such as certainly belongs to this species. 



Though not collected in a fresh state by me north of the Pribiloff Islands, 

 I have little doubt that broken valves found in bird-dung at Plover Bay, 

 near Bering Strait, are properly referable to this species. It is one of 

 the most abundant Alaskan Chitons, and grows to the length of an inch. 



The gill-rows extend forward for three-quarters the length of the foot, 

 each row containing twenty to twenty-five branchioe. The mantle -edge 

 is very narrow and -plum ; there is no veil, and the muzzle is i^lain, some- 

 Proc. Nat. Mus. 78 21 Feb. 14, 18 79. 



