LBFTOPLAX, 25 



Gem.> X. CALLOCIIIToN 



Valves rxp<>srd : insertion plates cut into num< ill rising 



from very *IHHHJ\J COVCS, the teeth more or les~ /mftressed at tin- out- 



side edges. Sutural-platet continuous acron the vr,r>/ nhullmr m*',/;,/,, 

 x/;//(.<. <;irdle typically covered with fine eompaet diamond -haped 

 scales : hut iii the suhgnms Stereochiton sparsely downv, fV-jinMit.Iv 

 naked ly erosion. 



Genus XI, ISCHNOCHITON Gray. 



Valves exposed ; insertion phites sharp, smooth ; eaves not 

 spongy, or rarely so. Umbo of posterior valve varying from pos- 

 terior to anterior. Girdle covered with imbricating scales. 



Genus V. LEPTOPLAX Carpenter, 1882. 



Leptoplax CPR. MS., and Table of Regular Chitons, 1871. DA i.i.. 

 Proc. U. S. Nat. Mus. 1882, p. 286. Type C. codrctatus Sby. 



Valves thin, partly immersed in the thin, smooth girdle. Inser- 

 tion plates acute, with few slits, but regular. Sinus scarcely toothed ; 

 mucro median. (Q?r.) 



The prominent characters of this genus are, (1) valves partly 

 covered by a thin extension of the girdle, (2) girdle smooth, as in 

 Tonicella, (3) insertion plates long, with few slits. The gills are 

 unknown. 



L. COARCTATUS Sowerby. PL 11, figs. 38, 39. 



Shell elongated, very delicate, little elevated, the dorsal ridge 

 acute ; greenish-ashen or reddish-olive. Valves of the normal form, 

 but two-thirds covered by a thin cuticle continued from the girdle. 

 Exposed portion of the valves flask-shaped, the jugular area smooth, 

 subelevated, having longitudinal rows of points; central areas and 

 end valves having large pustules, close and somewhat radiately 

 placed, about 20 on each side in a young specimen, 100 in an adult : 

 lateral areas scarcely defined ; mucro slightly behind the center, 

 rather elevated. Interior: Plates of insertion very long, 

 tinted, here and there delicately striated outside. Slits small, in the 

 posterior valve 6, posteriorly situated; central valves 1, anterior 

 valves 4, having shallow grooves running up to the cave-. Sinus 



