PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 325 



Touicella marniorea. 



Chiton latus Lowe, Zool. Jouin. ii, j». 103, pi. 5, f. 6-7, 1825. — Sowerby, Conch. 



111. Cliiton, f. 113, 1839. 

 Chiton fidminatus Couthoixy, Bost. Jouiii. Nat. Hist, ii, p. 80, pi. 3, f. 19, 1838. — 



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

 . Chiton pic.tus Bean, Tliorpe's Brit. Mar. Concli. p. 264, pi. — , f. 56, 1844. 

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

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

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

 Boreochiton 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. elougata, valvis ut in " Tracliydermon ruber" picturata; zona 

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

 satS, ; sinu angusto, altiore, Isevi. Lon. 40, Lat. 24 inm. 



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

 fi'om Massachusetts Bay northward to Greenland ; every part of the 

 North 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 tlie j)ilose gu'dle 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 veiy 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. 



Jefi'reys states that this may be identical with C. ptmctatus 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 Eussian 

 Tjapland. 



An attempt has been made to identify this species with 6'. ruber Lin., 

 but the examination of the Linnean Chitons by Mr. Hanley has left this 

 theory no sound foundation, and it hardly recpiires further notice. 



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

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

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



