ISCHNOCHITON-RADSIELLA. 143 



about 10 teeth by delicate slits. Anterior valve having 14-16, 

 central 2-3, posterior 22 slits. Teeth even and sharp, slightly 

 striated or grooved outside. Eaves solid. Girdle wide, flat, cov- 

 ered with solid, regularly and closely imbricating striated scales 

 (fig. 46). Length 35, breadth, 19 mill. 



Monterey, California. 



Chiton regularis CPU., P. Z. S. 1855, p. 232. Ischnoradsia 

 regularis CPU., MS. 



This species is of a very regular form, and a uniform drab, olive 

 or blue color. It is not closely allied to any other West Coast form. 

 The number of slits in the posterior valve is unusually large. 



I. TIGRINUS Krauss. PI. 19, figs. 60-63. 



Shell oblong, convex, roundly arched, buff-white, unicolored, or 

 striped lengthwise with reddish ; rarely roseate. 



Valves without apices. The lateral areas do not extend to the 

 middle of the back ; they are raised, and cut into radiating riblets 

 by 8 or 10 narrow impressed grooves, and there are rather con- 

 spicuous concentric wrinkles or waves of growth on the lower part 

 of the areas. The end valves are similarly sculptured. Central 

 areas closely and regularly pitted all over. Posterior valve rather 

 large and depressed, with subcentral umbo. 



Interior white and light brown. Anterior valve having 17-18, 

 central valves 2-3, posterior valve 12-13 slits; teeth rather thin, 

 but somewhat bevelled and roughened inside; eaves solid. Sinus 

 wide and flat, the sutural-plates being rounded. Muscle-scars dis- 

 tinctly impressed. 



Girdle rather wide, firm, densely clothed with somewhat convex, 

 finely striated scales (fig. 63). Length 22-28 mill. 



Cape of Good Hope. 



Chiton tigrinus KRAUSS, Die Siidafric. Moll., p. 38, t. 3, f. 5. 

 ? Ischnoradsia subcariosa CPR., MS. 



This species is readily known by its Radsioid valves and the 

 beautiful web-like sculpture of the central areas, produced by the 

 pattern of regularly arranged rhombic pits. It is like no other 

 species, although the young of J. magdalenensis bears a slight 

 resemblance in the sculpturing of the central areas. 



Although technically a Radsiella or Stenoradsia (it is not easy to 

 decide which) this species probably was developed from a different 

 stock of Ischnochitons. Indeed, the multiplication of side-slits may 



