320 PROCEEDINGS OF UKITED STATES NATIONAL MUSEUM. 



Lophyrns sp. G. O. Sars, 1. c. p. 114, not of Toll. 

 <BoreocMton G. O. Sars, 1. c. p. 115. 

 Leptochiton sp. auct. 



Char. — Laminse inserentes acutiB, Iseves; valvfe extns ct intus Iscli- 

 nochitoui exacte simulans; zona non porifera, squamulis mimitissiiuis 

 lai\abus coufertissime graniilata; branchiae breves. 



This name was originally proposed as a subgenus of Ischnochiton to 

 include Gray's second section, "mantle scales minute, granular" (P. Z. S. 

 1847, p. 147; Guide, p. 182, 1857). In 

 all other conchological characters, the 

 group accords \vith that genus, but the 

 animal differs in having the gills either 

 entirely jiosterior or reaching forward 

 from the tail only to about the middle 

 of the foot, while in Ischnochiton and 



. . Pig. E. — Toeth of Trachi/dcrmon cinercus 



Chiton they travel to its anterior ex- Lowe; after Loveu. 



tremity. These characters indicate a transition between the Ischnoid 

 and Leptoid Chitons by means of Trachydermon and Tonicella. Guilding 

 called the radulaof Chitons "Trachy derma"; but as the name has not 

 been adopted, no inconvenience is likely to ensue. (Cpr. MSS.) 



The genus is chiefly northern in its distribution. Chiton marginatm 

 of authors (Pennant's species being indeterminable) and C. cinereus (Linn.) 

 Lowe, are identical, according to Dr. Carpenter, the best authority on 

 the subject, as well as Hanley and others. The '■'■ Lepidoplcnrus'''' cinereua 

 of Sars is not the Linnean species, which is the type of Trachydermon, 

 l)ut a Leptochiton. His C rasped ochilus marginatus (whether the Chiton 

 marginatus of Pennant or not) is a Trachydermon, and not improbably 

 the true cinereus of Linne, which has been recognized, not from the 

 insufficient description in the Syst. Xaturae, but from his typical speci- 

 mens, through the invaluable labors of Mr. Hanley. 



Trachydermon ruber. 



Chiton ruher lAvrn. S. N. oil. xii, p. 1107, 1766. — Lowe, Zool. Jonrn. ii, p. 101, 



pi. 5, f. 2, 1825.— Gould, Iiiv. Mass. p. 119, f. 24, 1841.— Forbes & Hanley, 



Brit. Moll, ii, p. 399, pi. lix, f. G; AA, f. 6, 1853.— Hauloy, Shells of Lin. 



p. 17, 1855.— SoTvorby, Conch. III. Chiton, f. 103-4, 1839.— Reeve, Conch. 



Icon. Mon. Chiton, pi. 23, f. 175, 1847.— Jeffreys, Brit. Conch, iii, p. 224, 



1835; V, p. 199, pi. Ivi, f. 4, 18G9.— Binney's Gould's Inv. Mass. p. 280, f. 



523, 1870. 

 Chiton ci)iereusO. Fabr. Faun. Gronl. p. 423, 1780; not of authors, nor of Linn. ; 



lb. Dillwyn, Cat. Eec. 8h. p. 12, 1817. 

 Chiton minimus Spengler, Skrift. Nat. Selsk. iv, 1, 1797, fide Loven, not of 



Gmelin and Chemnitz. 

 Chiton Icevis Lov^n, Ind. Moll. Lit. Scand. p. 28, 1846; not of Montague, 



Forbes and Hanley, etc. 

 Chiton Iccms Pennant (i^robably), Brit. Zool. ed. iv, vol. iv, p. 72, pi. 36, f. '.\, 



nil (bad). 

 Chiton latus Leach, Moll. Brit. p. 231, 1852, Doc, fide Jeffiroys; not of Lowe, 



182.5. 



