324 PROCEEDINGS OF UMITED STATES NATIONAL MUSEUM. 



siibmediano, cpicibus promiueutibns ; ar. lat. inconspicnis ; tota super- 

 ficie qnincuiicialiter miiiute reticulata ; inhcs, v. ant. 16. post. 11^ ceutr. 

 2-tissata 5 dent, parvis lierspougiosis, late separatis ; subgrundis spon- 

 giosis, Curtis 5 siuu parvo; zona squamulis minutis obsita. Lou. 6, Lat. 

 3 mm. 



JTal). — Kyska Harbor, Kyska Id. Constantine and Kiriloff Harbors, 

 Amchitka Island, and i^azan 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 piu-plish red, with an ashy 

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

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

 line 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 ai^i^ears 

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

 cially under the eaves. The anterior slits are marked by i^diating lines 

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

 posterior valve, however, has not this aid to coimting, 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 TONICELLA Cpr. 



Tonicella Cpr. Bull. Essex lust, v, p. 154, 1873. Type T. maivnorea Fabr. 



Tonicia sp. Adams, Gray, Cpr. aud others. 



< Boreochiton G. O. Sars, Moll. Ref^. Arc. Norv. p. 116, Juue, 1878. 



YalvjB, mucro, laminte et sinus plerumque ut in Ischnochitoue ; zona 

 ut in Tonicia, coriacea, la?vis, seu subLTvis : branchire media?. 



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

 have often been referred, has pectinated insertion-plates and ambient 

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

 rows of gills. The two groups also <lilier in their dentition. The major 

 lateral of Tonicella is strongly tridentate ; in Tonicia the cusp of the 

 major lateral is scoop-shaped, rounded, with a plain edge, and the radula 

 recalls that of Chiton (typical) and Gorephium. Prof. Sars appears to 

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

 Chitons. 



Tonicella marmorea. 



Chiton marmoretts Fabricius, Fanu. Griiul. 420, 1780. — Jlidd. Mai. Ross, i, p. 103, 



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



Iviii, f. 2, pi. lix, f. 4, 1853.— Jeffreys, Brit. Couch, iii, p. 227, 18G5, v, p. 



199, pi. Ivi, f. 7, 1839. 

 CUton ruler Speugler, Skrift. Nat. Selsk. iv, p. 92, 1797.— Lov6u, lud. Moll. 



Scaud. p. 28, 184G ; uot of Liuue. 

 Chiton Iwvigaius Fleming, Ediu. Encycl. p. 113, t. vii; Brit. An. p. 290, 1828.— 



Reeve, Couch. Icon. Chitou, pi. 27, f. 179, 1847. 

 ? Chiton inmctatus Strom (Jeffreys)?, Acta Nidr. iii, p. 433, t. vi, f. 14. 



