288 * CALLISTOPLAX. 



structure, but without the pores, characterizes some species herein 

 referred to Chcetopleura. The posterior valve somewhat resembles 

 an irregular Maugerella; the anterior valve is strictly Acanthochi- 

 toid. Both of these are flattened, while the ridge is sharp on the 

 central valves. (Qpr.) 



Var. CALCULOSA Cpr. 



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

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

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

 the teeth all acute, but slightly roughened, hardly propped ; sinus 

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

 uous (Q>r.) 



Philippines (Mus. Cuming no. 79, part.) 



Angasia (? tetrica var.~) caleulosa CPE., 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 

 two 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 " ( Qpr.) 



Genus XXVII. CALLISTOPLAX Carpenter, 1882. 



Callistoplax CPR., Table of Kegular Chitons, 1873. Ball, Proc. 

 U. S. Nat. Mus. 1881, p. 283, 286 (Jan. 20, 1882). TRYON, 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- 

 iochiton, 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 Sowerby. PI. 61, figs. 17-26. 



Shell small, subelougate, slightly elevated, the jugum acute; 

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

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



