52 CALLOCHITON. 



Subgenus STEREOCHITON Carpenter. 



Stereochiton CARPENTER MS., 1871. DALL, Proc. U. S. Nat. 

 Mus. 1882, p. 286 (type C. castaneus Wood). 



Valves like Callochiton , but the girdle leathery and downy, the 

 scales very delicate and deciduous. In this group the teeth are 

 numerous, the median valves having 5 or more; but on account of 

 their narrowness they do not always have the lateral buttresses or 

 props outside, so characteristic of the teeth of the true Callochi- 

 tons. The eaves are very narrow, but distinctly porous or spongy, 

 as in Callochiton, and the bottoms of the slits are also coarsely 

 spongy. The sutural plates are continuous from side to side, the 

 median sinus being a mere wave, also a characteristic of Callochiton. 

 It is therefore obvious that the characters of the girdle alone sepa- 

 rate Stereochiton from Callochiton. In C. castaneus the girdle of 

 moderate sized specimens is always, so far as I know, denuded of 

 most of the covering of downy scales, but under a strong lens the 

 close, fine markings where they were inserted in the girdle may be 

 seen, as well as occasional scattered scales. 



Stereochiton externally resembles Tonicella, but it may be at once 

 distinguished from that group by its numerous side slits. 



C. CASTANEUS Wood. PI. 9, figs. 86-91. 



Shell oval, depressed, dark chestnut brown or variegated with 

 lighter brown. Jugum obtusely keeled ; lateral areas rather distinctly 

 defined, slightly raised. Entire surface very minutely, densely 

 granulated, when seen under a lens ; the granules low, not arranged 

 in distinct lines, but an obscure oblique radiation is more or less 

 visible. Growth striaB light. Umbo of the posterior valve some- 

 what in front of the middle, somewhat elevated. 



Interior rose colored; Anterior valve with 20, posterior with 18, 

 median valves with 5 deep slits. Teeth rather high and narrow,, 

 blunt, not propped, those of the terminal valves frequently bilobed 

 or trilobed inside, and obtusely crenulated at their apices. Inter- 

 stices spongy. Eaves very narrow, short, spongy. Sutural plates 

 connected, the jugal sinus shallow. Girdle leathery, bearing (when 

 not rubbed off) delicate elongated scales. 



Length 42, breadth 28 mill. 



Cape of Good Hope. 



Chiton castaneus WOOD, General Conchology, p. 13, t. 2, f. 2, 3 ; 

 t. 3, f. 2, 3, 1815. SOWERBY, Conchol. Illustr. f. 114, 115. REEVE, 



