PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 323 



liarity is that tlie central plates of the tail- valve are broken by serra- 

 tions, and that the scales are large and gravelly. 



The gills are twenty to twenty-five in number, the rows extending to 

 the head. Mantle-edge narrow, j)lain. There is no veil, and the semi- 

 circular muzzle is also plain. Anus terminal, papillate. Ovarian open- 

 ings single, on each side, the posterior end of the giU-row passing be- 

 hind them. The oviducts, as in some other species, could not clearly be 

 made out. The ovisac br ovary is irregularly shaped and single. 



The figure (pi. I, f. 9 a) strongly suggests that Prof. Sars, by inadvert- 

 ence in selecting a specimen for examination of the radula, got hold of 

 one of the extremely similar Leptochitons, since it does not resemble the 

 radula of T. albus, of which I have examined both American and Euro- 

 pean specimens. On the other hand, the not particularly commendable 

 figure of the radula of L. exaratus Sars looks more like alhus than any- 

 thing else. 



? Trachydernion lividus. 



. Chiton lividus Midd. Mai. Ross, i, p. 124, pi. xiii, f. 3 a-(/, 4, 1847.' 



Rab. — Sitka, Alaska Territory. 



This species (and C. scrobiculatus Midd. from California) probably be- 

 longs to this genus, but the descriptions and figiu'es are not sufficiently 

 clear to have admitted of their identification up to the present time. 

 The character most emphasized by Middendorf in C lividus is a key- 

 stone-Uke projection filling the anterior sinus between the two sutural 

 laminae. The specimen on which the description was based was a very 

 small and perhaps immature creature, with faint sculpture, somewhat 

 recalling Mop&lia Hindsii. 



Extra-limital Species. 

 Trachydermon cinereus. 



Chiton cinereus (Liu.) Lowe, Zool. Joum. ii, p. 99, 1825. — Forbes & Hanley, 



Brit. Moll, ii, 402, pL Iviii, fig. 1, 1853 (not of Sars). 

 Tradiydsnnon marginatus Cpr. New Engl. Chitons, 1. c. p. 153, 1873. 

 d'ospedodnhis marginatum Sars, 1. c. i>. 115, t. 20, f. 16 o-A, t. II, f. 2, 1878. 



Rob. — British and Scandinavian seas, north to Lofoten, south to Vigr»^ 



Bay, between tides and to the Laminarian zone. Type of the genus. 



, but 

 Trachydermon dentiens. .fofp 



Chiton dentiens Gld. Otia, pp. G, 242, 1862. " ' 



Ischnochiton (Trachydermon) pseudodentiens Cpr. Suppl. Rep. 1. c. p. 649, 186.* , . 



being 

 Rab. — Puget Sound and Vancouver Island. -imens 



The fact that the "teeth" are merely peculiar color-marks do^^^^ggjr^j^ 

 render it necessary to dispense with the original name of Dr. Goi 



Subgenus Traohyradsia Cpr. MSS. '^^er Lin., 



Trachydermon, valvis centralibus bi- sen pluri-fissatis. Typ^^ 

 fiiXgetrum Keeve. otice. 



i the length 



Traohyradsia aleutica. ^ Mantle- 



T. ahulica Dall, Proc. Nat. Mu.s. p. 1, Jan. 1878. '"muzzle iS 



T. t. parva, rufocinerea, oblonga, fornicata, jugo acutissimo j 



