ISCHNOCHITON. 77 



I. RETEPOROSUS Cpr. PI. 16, figs. 47, 50, 51, 52, 53. 



The original description will be found on p. 75 of vol. xiv. 



The shell is rather elevated, distinctly carinated, the side-slopes 

 nearly straight. The color is either (1) dull buffish gray white 

 touched with reddish orange at each beak, or (2) a very pretty shade 

 of reddish-purple, uniform or with a white dorsal stripe and some faint 

 light spots ; in either case the girdle is of the same color as the valves, 

 with or without black scales scattered over it. The valves are parti- 

 ally covered by a black deposit in all of the individuals seen. 



The slight beaks of the median valves do not modify the slightly 

 concave contour of the posterior border. The lateral areas are not 

 raised; sculpture consisting of a variable number (generally 4-7) of 

 rather acute radiating riblets (spreading somewhat like those of a 

 Pinna) bearing sparsely scattered, minute pustules which are often 

 lacking on some or all valves ; the intervals between riblets finely 

 granulated. Central areas sculptured with a very beautiful and 

 clearly-cut pattern of squarish pits or cells formed by the crossing of 

 fine forward-converging riblets by others curving in a radial direction 

 (fig. 47). Anterior valve having many narrow radial riblets, like 

 those of the lateral areas, some of them generally with minute pust- 

 ules. Posterior valve (figs. 51, 52) having the mucro in front of the 

 middle. 



Interior bluish-white or pink. Anterior valve having 11, median 

 valves 1 -1, posterior valve 1 1 slits. Sutural lamince low and rounded, 

 continuing in a narrow lamina across the shallow, wide, gently rounded 

 sinus. 



Girdle covered with solid rather flattened scales measuring about 

 one-sixth of a mill, in breadth, and coarsely, deeply striated (fig. 50). 



Length 15, breadth 8 mill.; divergence 95-100. 



San Pedro, California (Cooper) ; Victoria B. C., 15 fms. (C. F. 

 Newcombe.) 



The type (Mus. Smiths. lust, 14917) is a light colored specimen, 

 touched with orange at the beaks, as first described above. Others 

 before me from Victoria B. C. have the same coloration, but most of 

 those I have seen from Victoria are purple. The small acute pust- 

 ules of the lateral areas are very variable, often entirely wanting. 

 The delicate riblets of the lateral areas are generally more numerous 

 than shown in fig. 47, which is drawn from Carpenter's type ; they 

 have a strong tendency to split. 



