2 THE NAUTILUS. 



Tonicella. Carpenter, Bull. Essex Inst. V, p. 154, 1873 (Chiton 



marmoreus Fabricius) . 

 Boreochiton G. O. Sars, Moll. Reg. Arct. Norv., p. 116, 1878 



(Chiton ruber L., and C. marmoreus Fabriciua). 

 TonitieUa Thiele, Gebiss d. Schnecken, II, p. 389, 1891 (T. 



marmorea Fabr.) , 



Section Cyanoplax Pilsbry. 



Cyanoplax Pilsbry, Man. XIV, pp. 40, 44, 1892 (Chiton hart- 

 wegii Carpenter). 



Submenus Spongioradsia Pilsbry. 



Spongioradsictr Pilsbry, Man. XV, p. 65, 1894 (Trachyradsia 

 aleutica Dall). 



In view of the similarity of names the following synonymy 

 may be useful : 



Genus LEPIDOPLEURUS Risso. 



Lepidopleurus (Leach Ms.) Risso. Hist. Nat. Eur. Merid. IV, 

 p. 267, 1826 (1st sp. L. cayetcmus (Poli) Risso) ; G. 0. 

 Sars, MoU. Reg. Arct. Norv., p. 110, 1878. 



Section Leptochiton Gray. 



Leptochiton Gray, P. Z. S., 1847, p. 127 (Chiton cinereus Mon- 

 tagu (not Linne) = C. asellus Spengler) ; Carpenter, 

 Suppl. Rep. Brit. Assoc., pp. 530, 612, 650, 1864 (1st sp. 

 mentioned as a real member of the genus is Leptochiton 

 nexus Carpenter). 



? Lepidochiton Carpenter, Rep. Brit. Assoc., pp. 317, 349, 

 1857 (1st sp. C. lividus Midd.). Includes also C. inert en- 

 sii Midd., C. scrobiculatus Midd., and C. proprius Reeve ; 

 the latter = C. dispar Cpr., not Sowerby. 



I confess to an inability to get anything like systematic 

 order out of Middendorff's extraordinary tangle of names, 

 except where some subsequent author has fixed a species as 

 type, as in the case of Symmetrogephyms (Midd., Feb. 1848), 

 which Chenu (Man., p. 383) has declared to be typified by 



