PROCEEDINGS OP UNITED STATES NATIONAL MUSEUM. 325 



Tonicella marmorea. 



Chiton latus Lowe, Zool. Journ. ii, p. 103, pL 5, f. 6-7, 1825.— Sowerby, Conch. 



111. Chiton, f. 113, 1839. 

 Cliiton fidminatus Coutkoiiy, Bost. Journ. Nat. Hist, ii, p. 80, pi. 3, f. 19, 1838.— 



Gould, Inv. Mass. i, p. 148, f. 3, 1841. 

 Chiton pictus Bean, Thorpe's Brit. Mar. Conch, p. 264, pi. — , f. 56, 1844. 

 Chiton Flemingim Leach, Moll. Gt. Brit. p. 230, Dec. 1852. 

 Tonicia marmorea H. & A. Adams, Gen. Rec. Moll, i, p. 474, 1854. 

 Tonicella marmorea Carpenter, Bull. Essex Inst, v, p. 154, 1873. 

 Borcochiton marmoreus G. O. Sars, Moll. Reg. Arct. Norv. p. 116, t. 8, f. 3 a-l, 



t. II, f. 4 (not good), 1878. 



T. t. elongata, valvis ut in " Trachyderinon ruber" picturataj zona, 

 coriacea, expansa, laevij intus, v. post. 8-9, v. ant. 8-10, v. centr. 1-fis- 

 sata; sinu angusto, altiore, la3vi. Lon. 40, Lat. 24 mm. 



Sal). — Aleutian Islands, 8-10 fins., rare; east coast of ]North America 

 from Massachusetts Bay northward to Greenland ; every part of the 

 Xorth Atlantic north of Great Britain, and as far south as Dublin Bay 

 on the west and the shores of Holland on the east ; in 5-100 fathoms, 

 according to temperature. 



This well-known species has almost exactly such a color-pattern as 

 Tracliydermon ruber, and in dry specimens the pilose girdle of the latter 

 is the most convenient means of distinction. A comparison of European 

 with Greenland specimens shows that the latter are usually more ele- 

 vated, and the posterior valve has usually seven slits instead of eight or 

 nine. This form, of course, is the typical one ; those from Europe may 

 perhaps retain the varietal name of T. latus Lowe. The Alaskan speci- 

 mens, as is often the case with mollusca of this region, are more like 

 European than East American specimens, and in the fresh condition ex- 

 hibit a very broad, smooth, yellowish girdle, sometimes as wide on each . 

 side of the valves as the whole width of the shelly part. Otherwise they 

 agree with Norwegian specimens. The measurements given above are 

 for the very largest; they average about an inch in length. It doubtless 

 extends to the Arctic Ocean on the shores of Alaska, though all our 

 specimens happened to come from the Aleutians. 



Jeffreys states that this may be identical with C. punetatus Strom, but 

 the name would be an evident misnomer, as it is in no way punctate, 

 and the identification requires further confirmation. 



Middendorf found a variation in the number of anterior slits, being 

 five to seven, and in posterior slits six to nine, in all, in the specimens 

 he examined, which came from the White Sea and Arctic coast of Russian 

 Lapland. 



An attempt has been made to identify this species with C. ruber Lin., 

 but the examination of the Linnean Chitons by Mr, Hanley lias left tin's 

 theory no sound foundation, and it hardly requires farther notice. 



The gill-rows of this species extend forward three-quarters the length 

 of the foot, and each contains twenty to twenty-five branchiae. Mantle- 

 edge plain, inconspicuous, very narrow. The margin of the muzzle is 



