86 I-i 'UNIX IIIToN. 



racliately costulate, decussated by concentric growth sulci, the rib- 

 It -ts more or less scaly-gran ose, the interstices very delicately punc- 

 tate. Central areas longitudinally wrinkled, the interstices deli- 

 cately punctate. Mucro sulx-entral. Anterior valve having 16, 

 median valves 4, posterior valve 12 slits. Sutural plates yellowisli- 

 rose color. Girdle half as broad as the lateral slope of the valves, 

 very delicately granulose, blackish-green maculated with white. 

 Gills ambient, composed of 44 branchue. 

 Length 44 mill. ; divergence 130. 



Bay of Hakodadi, 



Chiton lindJiolmi SCHRENCK, Bull. 1'Akad. Imp. Sci. de St. 

 rsb. v. p. 511 ; Melanges Biolog. iv, p. 253; Reiseu u. Forsch. 

 im Amurlande ii, Zool. p. 288, t. 12, f. 9-16. 



This large radsioid species may prove to be a Stenoradsia (see p. 

 61) ; but the meagre description of the girdle given by Schrenck, 

 causes me to place it, for the present, in the decidedly heterogenous 

 group Trachyradsia. 



Subgenus VI. ISCHNOCHITON Gray (restricted). 



Ischnochiton GRAY, P. Z. S. 1847, p. 126. SHUTTLEWORTH, 

 Bern. Mittheil. 1853, p. 66. Lepidopleurus (part) H. & A. ADAMS, 

 and CARPENTER, olim., not Lepidopleurus Risso. Ichsnochiton 

 FISCHKK, Manuel p. 880. 



Valves having sharp, non-pectinated insertion plates ; mucro 

 median or anterior; girdle covered with imbricating scales. 

 Within this subgenus three subdivisions may be recognized : 



Section Ischnochiton s. s., in which the valves and insertion plates 

 are thin and smooth, one side-slit in each median valve ; the 

 scales of the girdle flat and striated. 



Section Lepidozona, differing in the convex, solid girdle scale-. 

 which are usually almost smooth. 



Section Radsiella, like typical Ischnochiton except that there are 

 two or several side-slits in each median valve. 



The .-nbgenus Heterozona should properly be included here also, 

 and Ischnoradtio is not far removed from Lepidozonn in characters. 



