320 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



Lophyrua sp. G. O. Sars, 1. c. p. 114, not of Poll. 

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

 Leptockiton sp. auct. 



CJiar. — Laminae inserentes acntse, laeves; valvre extus et intus Isch- 

 nocbitoni exacte siiuulansj zona non porifera, squamulis minutissimis 

 laevibus confertissime granulata; braucliine breves. 



This name was originally proposed as a snbgenns of Ischnochiton to 

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

 a847, p. 147; Guide, p. 182, 1857). In 

 all other conchological cliaracters, the 

 group accords with that genus, but the 

 animal differs in having the gills either 

 entirely posterior or reachiug forward 

 from the tail only to about the middle 

 of the foot, while in Ischnochiton and 



„, .. ,, . -, . ., . . Fig. E. — Teeth of Trachiidermon cinereus 



Chiton they travel to its anterior ex- Lowe; after Lov§n. 



tremity. These characters indicate a transition between the Ischnoid 

 and Leptoid Chitons by means of Trachydcrmon aiid Tonicella. Guilding 

 called the radula of Chitons "Trachyderma"; 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 marginatus 

 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 Hauley and others. The '■'■Lepidoplcurus'''' cinereus 

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

 but a Leptochiton. His Craspedochilus marginatus (whether the Chiton 

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

 the true cinereus of Linn(^, which lias been recognized, not from the 

 insufdcient description in the Syst. Naturae, but from his typical speci- 

 mens, through the invaluable labors of Mr. Hanley. 



Trachydermon ruber. 



Chiton ruber Ijiuu. S. N. ed. xii, p. 1107, 176G. — Lowe, Zoiil. Journ. ii, p. 101, 



pi. 5, f. 2, 1825.— Gould, Inv. Mass. p. 149, f. 24, 1841.— Forbes & Hanley, 



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



p. 17, 1855.— Sowerby, Concb. 111. Chiton, f. 103-4, 1839.— Reeve, Conch. 



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



1865; V, p. 199, pi. Ivi, f. 4, 18G9.— Binney's Gould's Inv. Mass. p. 260, f. 



523, 1870. 

 Chitoti cinereus 0. Fabr. Faun. GriJul. p. 423, 1780: not of authors, nor of Linn. ; 



lb. Dillwyn, Cat. Eec. Sh. p. 12, 1817. 

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



Gmelin and Chemnitz. 

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



Forbes and Hanley, etc. 

 Chiton lajvis Pennant (probably), Brit. Zool. ed. iv, vol. iv, p. 72, pi. 36, f. 3, 



1777 (bad). 

 Chiton Iatu3 Leach, Moll. Brit. p. 231, 1852, Dec, fide Jeffreys; not of Lowe, 



1825. 



