94 ISCHNOCHITON. 



/ 



in the sinus is perhaps accidental, from their being older specimens. 

 (Cpr.} 



C. decussatus Reeve. (PI. 23, figs. 83, 84.) Shell oblong-ovate, 

 a little attenuated posteriorly. Terminal valves and lateral areas 

 grained, the grains rather obtuse, numerous, irregular, interstices 

 rough. Central areas decussated with very close slightly wrinkled 

 striae. Pale yellowish-green, flamed along the summit with brown. 

 (Bte.) 



Australia (Mus. Cuming, 1 specimen). 



C. castus Reeve. (PI. 23, figs. 87, 88.) Shell oval, subelongate, 

 rather elevated, orange tinted with red ; jugum acute ; mucro rather 

 raised, median, the slope behind it concave. Central areas closely 

 wrinkled, the wrinkles at the jugum diverging laterally, sometimes 

 interrupting one another and forming zigzags. Lateral areas and 

 end valves with concentric nodular wrinkles, sometimes the wrinkles, 

 sometimes the nodules predominating ; nodose at the sutures. 



Interior orange-flesh tinged ; front valve with 9, central 1, poste- 

 rior 13 slits ; teeth acute, scarcely pectinated ; sinus wide, flat, deep, 

 slightly and very minutely denticulated by the external sculpture ; 

 eaves large, hardly spongy. 



Girdle olivaceous, slightly tessellated, imbricated with large, 

 wide and solid, deeply striated scales. Length 21, breadth 12 mill. ; 

 divergence 103. (Cpr.,from type specimen.} 



Australia. 



The general characters of this species are the same as in textilis 

 and cariosus, but it differs sufficiently in sculpture. Both of the 

 two specimens in the Brit. Mus. are curved up so that they cannot 

 be measured accurately. 



Another form which Carpenter described in MS. as " I. castus n. 

 sp.," but which he afterward decided to be synonymous with castus 

 Rve., is white with a black girdle. The shell is much elevated with 

 acute jugum ; the central areas have delicate but much raised line, 

 about 30 on each side, and subparallel except toward the ridge 

 where they bend outward, and upon the jugum they are elegantly 

 undulating. The lateral areas and end valves have rather large, 

 separated grains, scarcely radiating, serrating the sutures. The 

 anterior valve has 13, central 1, posterior valve 11 slits. The 

 girdle is clothed with narrow, stout, deeply grooved scales. Length 

 30, breadth 16 mill.; divergence 110. It is from Swan River 

 (Mus. Cuming, No. 100). 



