324 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



submediano, apicibus prominentibus ; ar. lat. inconspicuis ; tota super- 

 ficie quincimcialiter miiiute reticulata; intus, v. ant. 16, post. 11, centr. 

 2-fissata ', dent. i)arvis perspongiosis, late separatis ; subgrimdis spon- 

 giosis, Curtis ; sinu parvo ; £ond squamulis minutis obsita. Lon. C, Lat. 

 3 mm. 



Sab. — Kyska Harbor, Kyska Id. Constantine and Kiriloft' Harbors^ 

 Amcbitka Island, and Nazan Bay, Atka, m the Western Aleutians, at 

 low- water mark, under stones on the beach, Dall ! Fifteen examples. 



This modest little species is of a dull livid purj)lisli red, with an ashy 

 tinge, especially on the narrow girdle. Except for the well-marked 

 ridges of growth, it appears smooth, but possesses (like all Chitons) a 

 fine reticulation, only visible under a magnifier. The lateral areas are 

 not distinct, the back is very much rounded, and the valves well hooked 

 in the median line. The substance of the valves from within appears 

 remarkably spongy, as if rotten, or even like vesicular pumice, espe- 

 cially under the eaves. The anterior slits are marked by radiating lines 

 of holes, though the teeth between them can hardly be made out. The 

 posterior valve, however, has not this aid to counting, and in the general 

 sponginess it is almost impossible to say how many teeth or denticles 

 exist. It bears no marked resemblance to any other species of the re- 

 gion. 



Genus TOmCELLA Cpr. 



Tonicella Cpr. Bull. Essex Inst, v, p. 154, 1873. Type T. marmorea Fabr. 



Tonicia sp. Adams, Gray, Cpr. and otherH. 



< Boreochiton G. O. Sars, Moll. Roii. Arc. Norv. p. IIG, June, 1878. 



Valv8B, mucro, laminae et sinus plerumque ut in Ischnochitone ; zona 

 ut in Tonicia, coriacea, Isevis, seu sublsevis : branchiae mediae. 



The genus Tonicia Adams and Gray, to which the species of Tanicella 



have often been refeiTed, hsis pectinated insertion-plates and ambient 



gills like the typical Chitons, while Tonicella has sharp plates and short 



rows of giUs. The two groups also diller in their dentition. The major 



5ral of Tonicella is strongly tridentate : in Tonicia the cusp of the 

 souti "-^ '^ I A 



>r lateral is scoop-shaped, roimded, with a plain edge, and the radula 



^s that of GJiiton (typical) and Corephimn. Prof. Sars ajjpears to 



'^been unaware of Dr. Carpenter's publication on the New England 



-oJTCtlC 



IS 



to Atti 



and fo^}^ marmorea. 



The av'**^"" mannoreiis Fabricius, Fauu. Grciul. 420, 1780. — Midd. Mai. Eoss. i, p. 103, 

 ,, , , "^ 1847; Sib. Keise, 182, 1851.— Forbes & Hanley, Brit. Moll, ii, p. 414, pi. 

 tne Old na ^^jjj^ ^ ^^ ^^ ^.^^ ^ ^^ 1853.— Jeffreys, Brit. Couch, iii, p. 227, 1865, v, p. 



known and 199, pi. ivi, f. 7, 1839. 



•water AlaSoH ruber Speugler, Skrift. Nat. Selsk. iv, p. 92, 1797.— Lov6n, Ind. Moll. 



of the girdl<?caud. p. 28, 1846 ; not of Linne. 



be urobablv'* Icenigatus Flemiug, Edin. Encycl. p. 113, t. vii; Brit. An. p. 290, 1828. — 



}, "^tieeve, Conch. Icon. Chiton, pi. 27, f. 179, 1847. 



It seems 'ton pimctatus Strom (Jeffreys)?, Acta Nidr. iii, p. 433, t. vi, f. 14. 



