PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 323 



liarity is that the 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, plain. 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 gill-row passing be- 

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

 made out. The ovisac or 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 albus than any- 

 thing else. 



? Trachydermon lividus. 



Chiton lividus Midd. Mai. Eoss. i, p. 124, pi. xiii, f. 3 a-g, 4, 1847. 



Sab. — Sitka, Alaska Territory. 



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

 longs to this genus, but the descriptions and figures 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-like 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 2Iopalia Hinds ii. 



Extra-limited Species. 



Trachydermon cinereus. 



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



Brit, Moll, ii, 402, pi. lviii, fig. 1, 1853 (not of Sars). 

 Trachydermon marginatus Cpr. New Engl. Chitons, 1. C. p. 153, 1873. 

 Craspedochilus marginatus Sars, L c. p. 115, t. 20, f. 16 a-h, t. II, f. 2, 1878. 



Hab. — British and Scandinavian seas, north to Lofoten, south to Vigo 

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



Trachydermon dentiens. 



Chiton dentiens GUI. Otia, pp. 6, 242, 1862. 



Ischnochiton (Trachydermon) pseudodentiens Cpr. Suppl. Rep. L e. p. 649, 1863. 



Hab. — Puget Sound and Vancouver Island. 



The tact that the "teeth" are merely peculiar color-marks docs not 

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



Subgenus TRACHTRADSIA Cpr. MSS. 

 Trachydermon, valvis ceutralibus bi- seu pluri-lissatis. Type Chiton 

 fulgetrum Reeve, 



Trachyradsia aleutica. 



T. aleutica . Dall, Proc. Nat. Mus. p. 1, Jan. 1878, 



T. t. parva, rufocinerea, oblouga, fornicata, jugo acutissimoj mucrone 



