82 ISCHNOCHITON. 



everywhere minutely punctured. The lateral areas are very 

 abruptly and distinctly elevated, regularly ridged by the obtusely 

 rounded stages of growth and bearing a few scattered granules. 

 Central areas with the lines of increase well marked, and remark- 

 ably barred with about six elevated, longitudinal, parallel ridges, 

 which are generally dislocated about the middle by some of the 

 lines of increase. The posterior valve has a very minute, and 

 acute, nearly central umbo, with an abrupt depression passing 

 transversely through it ; the margin is very minutely imbri- 

 cated by prismatic scales, colored like the shell, and with yellowish 

 bands crossing it, opposite to the junctures of the valves. (Old.*) 



Length 12J, breadth 7* mill. 



Orange Harbor, Terra del Fuego. 



Ch. puniceus (CouTHOUY MS.') GOULD. Proc. Bost. Soc. N. H. ii, 

 1846, p. 143 ; Exped. Sh. p. 5 ; U. S. Expl. Exped. Moll. p. 324, t. 

 27, f. 412; Otia Conch, p. 5. Trachydermon ruber var., CARPEN- 

 TER MS. Lepidopleurus puniceus ROCHEBR., Miss. Sci. Cap Horn, 

 Moll. p. 140. 



The gills extend forward to the middle of the foot. They are 

 erroneously represented upon Gould's plate. Carpenter considered 

 this a synonym of T. ruber, but it is probably distinct. 



I. STEINENII Pfeffer. PL 6, figs. 19, 20, 21. 



The form of the animal is a somewhat elongated oval, bluntly 

 rounded before and behind, the middle keel-like and elevated. 

 Girdle covered with granules which are somewhat elongated in a 

 radial direction. Eighteen gills on each side, reaching from the 

 middle of the foot nearly to the posterior end. 



Shell rather elevated, very finely granulated. Median valves 

 comparatively narrow, their length not much over J of their 

 breadth, the posterior angles not produced backward; younger 

 examples having strong, acute apices, older having less projecting 

 blunt apices. Lateral areas separated from central areas by a dis- 

 tinct ridge. Central areas having transverse lines of fine grains, 

 which turn at right angles and become longitudinal on the lateral 

 areas; there are also more or less terrace-like marks of growth- 

 arrest. There is a system of weak radial wrinkle-striae, converging 

 toward the umbo, upon the central areas, more developed in young 

 specimens, and totally absent in the larger ones. Anterior valve 

 half-round, concentrically finely granulated, and having coarse con- 



