ISCHNOCHITON. 69 



Length 12*, breadth 7* mill. 

 Length 18, breadth 10* mill. 



British and Scandinavian .Seas, north to Lofoten, south to Bay of 

 Kiel and Vigo Bay. 



Chiton cinereus LINNE, Syst. Nat. xii, teste Hanley, Ipsa Linnsei 

 Conch, p. 17. LOWE, Zool. Journ. ii, p. 99, 1825. FORBES & 

 HANLEY, Hist. Brit. Moll, ii, p. 402, t. 58, f. 1, ((7. marginatus on 

 plate). C. marginatus PENNANT, Brit. Zool. iv, p. 71, t. 36, f. 2, 

 and of MONT., Sows., RYE. and JEFFREYS, Brit. Conch, iii, p. 221, 

 t. 56, f. 5; P. Z. S. 1882, p. 669. C. marginatus MEYER & 

 MOBIUS, Fauna der Kieler Bucht, ii, t. 1, f. 1-5. Craspedochilus 

 marginatus BARS, Moll. Arct. Norv. p. 115, t. 20, f. 16 ; t. 2, f. 2. 

 Trachydermon marginatus CPR., New Eng. Chitons, p. 153. 

 Trachydermon cinereus CPR. MS. p. 15. DALL, Proc. U. S. Nat. 

 Mus. 1878, p. 323. NOT Lepidopleurus cinereus SARS, /. c., t. 7, f. 

 8. Chiton circumvallatus REEVE, Conch. Icon. t. 27, f. 168. 



This species may be known by the evenly shagreened surface, 

 which is quite different from other North Atlantic Trachydermons. 

 Tr. dentiens Old., which Jeffreys considers the same as cinereus, 

 differs in sculpture, color, and the shorter form. There are a num- 

 ber of old and more or less doubtful synonyms, such as Ch. 

 fuscatus Brown, 111. Conch. G. B. p. 66, t. 21, f. 17 ; and Jeffreys 

 quotes also cimex Chemn. and cimicinus Landt. 



Carpenter seems to have supposed that the gills of this species 

 did not extend forward beyond the middle of the foot, but I have 

 determined by the examination of alcoholic specimens, one of which 

 is drawn on pi. 7, fig. 57, that they extend nearly to the head, 

 being composed of 16 or 17 plumes on each side. They are also so 

 figured by Meyer & Mobius. In this character, cinereus differs 

 from albus and ruber, in which species the gills are median. 



Carpenter, having examined the type of C. circumvallatus Rve., 

 writes that he is satisfied that it is merely a cinereus. The locality 

 given by Reeve is no doubt wrong. 



Var. variegatus Phil. PI. 7, figs. 58, 59, 60. 



Smaller, with triangular sutural laminse. Anterior valve having 

 8 or 9, posterior valve having 7 or 8 slits in the insertion plates. 

 Length 8, breadth 5, alt. 3 mill. 



Mediterranean and A driatic Seas. 



