288 CALLISTOPLAX. 



structure, l)ut \vitliout the purrs, characterizes some B '-rein 



referred to r/m/i,y>/,-*//v<. The posterior valve somewhat reseml>lrs 



an irregular M '/ : the 1 anterior valve is strictly Acanthochi- 



toid. Both of tlu-se an- flatt< m-d, while the ridge is sharp on the 

 .il valves. (Cpr.) 



Yar. < AI.CULOSA Cpr. 



Shell externally very similar to . 1 . tetrica, but roseate ; jugal areas 

 distinctly tricostate ; anterior valve distinctly five-angled; pebble- 

 sculpture smoother. Interior: posterior valve normal, with 5 slits, 

 t la- teeth all acute, but slightly roughened, hardly propped; sinus 

 narrow, deep, smooth, flat. Bunches of spicules minute, inconspic- 

 uous (Cpr.) 



J'/ti/ijijtitte* (Mus. Cuming no. 79, part.) 



An(/'i.in (/ tetrica war.') <-nl<-ul<>sa CPR., MS. 



" The insertion plates of this shell offer a marked contrast to the 

 Cingalese shell, being strictly like Ischnochiton (with shortened 

 eaves) throughout. But one specimen, after an anterior fracture, 

 has mended it with distinctly rugulose teeth, and made its posterior 

 teeth propped and lobed, showing a close connexion between the 

 tw<> forms. It is probable that Mr. Cuming''s specimens from the 

 two localities had been intermixed. The tufts could scarcely be 

 detected in shriveled specimens " (Cpr.} 



Genus X XVII. CALLISTOPLAX Carpenter, 1882. 



CPR., Table of Regular Chitons, 1873. Dall, Proc. 

 U. S. Nat. Mus. 1881, p. 283, 286 (Jan. 20, 1882). TRYOX, Struct. 

 and Syst. Conch, ii, p. 342. 



Valves outwardly and within as in Callistochiton. Girdle naked 

 except for a series of bristle-bearing pores. 



The present genus is one of the very few which rest entirely upon 

 characters of the girdle ; but so different is this from that of Callis- 

 tnchiion. not only in the presence of pores, but in the entire absence 

 of scales, that no course seems open but to treat the group as of 

 generic value. 



C. RETUSUS Sowerl>y. PI. fll, figs. 17-26. 



Shell small, subeloniraU , -lightly elevated, the jugum acute; 

 mucro median, vory obtuse, elevated in adult specimens. Jugal 

 area smoothish, granulose, in the adult having a few acute longitu- 



