276 CALLISTOCHITON. 



The only published figure of this species is very poor. Smith 

 writes : closely allied to C. antiquus, but it is differently and mora 

 finely sculptured, and the scales on the mantle are larger. 



The type is in the British Museum. 



C. ADENENSIS Smith. PL 59, fig. 45. 



Shell small, depressed, hardly carinated, unicolored pale brown- 

 ish. Anterior valve having about 22 granulate radiating ribs. 

 Lateral areas composed of two strong granulate ribs ; central areas 

 longitudinally granose-lirate, the lirse more delicate in the middle 

 than at the sides. Posterior valve having about 25 delicate granulate 

 lirce. Girdle pale brownish, very minutely scaly. 



Length 14, breadth 91 mill. (Smith.) 



Aden. 



Chiton ( Callistochiton') adenensis E. A. SMITH, Proc. Zool. Soc. 

 Lond. 1891, p. 421, t. 33, f. 7. 



The sculpture of this species is of the same character as that of C.. 

 antiquus Reeve, but not quite so pronounced, and the rays of both 

 the terminal valves are more numerous. (Smith.') 



The type is in the British Museum. The italics of the above 

 description are my own. 



C. HETERODON Pilsbry, n. sp. PI. 60, figs. 11-15. 



Shell oblong, rather elevated, carinated, the side-slopes nearly 

 straight ; buff-white, sparsely dotted on the ridge with olive-black 

 and having one or two spots of the same on the sides of each valve ; 

 the girdle yellowish, having narrow slate-colored bars. 



Valves having rather acute but not backward-projecting beaks. 

 Lateral areas raised, having 3 or 4 ribs, being primarily divided by 

 a deep sulcus into two ribs, the posterior of which is again divided ; 

 and sometimes the front rib also is split into two, especially on the 

 second valve ; the interstices are coarsely pitted, and the posterior 

 rib is ribbed across, dentating the sutures. The central areas have 

 about 11 rather narrow but strong longitudinal riblets on each side of 

 a wider dorsal rib ; the interstices nearly smooth. Head valve having 

 11 (or 13, by splitting) strong denticulate ribs. Tail valve narrower 

 than the head-valve, not depressed, the mucro obtuse, post median; 

 posterior slope convex, having 11 radiating ribs. 



Interior pure white. Sutural plates narrow, separated by a square, 

 slightly deticulate sinus, which is distinctly laminate and slightly 

 notched at the corners. Anterior valve having 8, central valves 1, 



