86 ISCHNOCHITON. 



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

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

 tate. Central areas longitudinally wrinkled, the interstices deli- 

 cately punctate. Mucro subcentral. Anterior valve having 16, 

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

 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 branchiae. 

 Length 44 mill. ; divergence 130. 



Bay of Hakodadi, Japan. 



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

 Petersb. v, p. 511 ; Melanges Biolog. iv, p. 253; Reisen u. Forsch. 

 iin 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 heterogeuous 

 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 

 FISCHER, 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 scales, 

 which are usually almost smooth. 



Section Radsiella, like typical Ischnochiton except that there are 

 two or several side-si its in each median valve. 



The subgenus Heterozona should properly be included here also, 

 and Ischnoradsia is not far removed from Lepidozona in characters. 



