PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 323 



liarity is tliat tlie ceutral i>lates of the tail-valve arc broken by serra- 

 tions, and tliat the scales are large and gravelly. 



The gills ai-e twenty to twenty-live in number, the rows extending" to 

 the head. Mantle-edge narrow, plain. There is no veil, and the semi- 

 eircular muzzle is also i^lain. Anns terminal, papillate. Ovarian open- 

 ings single, on each side, the posterior end of the gill-row i)assing be- 

 hind them. The OAidncts, 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 exti'emely similar Leptochitons, shice it does not resemble the 

 radnla of T. alhus, 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- 

 thuig else. 



? Trachydermon lividus. 



Chiton lividus MidiL Mai. Eoss. i, p. 124, i)l. xiii, f. 3 a-g, 4, 1847. 



Hah. — Sitka, Alaska Territory. 



This species (and C scrohicidatns 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-like projection filling the anterior sinus between the two sutiiral 

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

 small and perhaps immature creature, with faint sculptiu-e, somewhat 

 recalling 2Iopalia 'Hindsii. 



EMra-limital Species. 

 Tracliydermon cinereus. 



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



Brit. Moll, ii, 402, pi. Iviii, tig. 1, 1853 (not of Sars). 

 Trachydermon inarginatus Cpr. New Engl. Chitons, 1. c. p. 153, 1873. 

 Craspedochilus marginatus Sars, 1. c. p. 115, t. 20, f. 16 a-h, t. II, f. 2, 1878. 



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

 Bay, between tides and to the Lamiuarian zone. Tyjie of the genus. 



Trachydermon dentiens. 



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



Ischnochiton (Trachi/dermon) pseudodentiens Cpr. Suppl. Rep, 1. c. p. 649, 1863. 



Hah. — Puget Sound and Vancouver Island. 



The fact that the "teeth" are merely peculiar color-marks does not 

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



Subgenus Trachyradsia Cpr. MSS. 

 Tracliydermon, valvis centralibus bi- sen pluri-fissatis. Tyx)e Chiton 

 fulgcfrum Reeve. 



Trachyradsia aleutica. 



T. aleiUica Dall, Proc. Nat. JIus. p. 1, Jan. 1878. 



T. t. parva, rufocinerea, oblonga, fornicata, jugo acutissimo ; mucrone 



