62 ISCHNOCHITON. 



still to see specimens truly connecting the three forms, although 

 they are doubtless closely allied. The present form differs from 

 magdalenensis in having a concave head valve, strong, distinct, 

 acute riblets upon the central areas, and a generally more robust 

 growth. 



I. conspicuus also has a concave head valve, but the sides of the 

 central areas show no sculpture except microscopic granulation, 

 and the scales of the girdle are pulled out into true spines or bris- 

 tles. 



There is a light form of acrior which is fleshy- white, the girdle 

 gray- white or dark ; and some of these have the jugum or the cen- 

 tral areas of the normal green-olive color (fig. 89.) 



I. MAGDALENENSIS Hinds. PI. 15, figs. 98, 99, 100. 



Shell elongated, rather narrow, generally faintly mottled with 

 delicate olive on a light greenish, blue or pinkish ground. Interior 

 bluish, white or pink. Lateral areas and end valves having radia- 

 ting riblets, central areas finely pitted. 



The lateral areas are distinctly raised, radiately delicately ribbed. 

 Front slope of the anterior valve straight. Central areas having a 

 more or less developed system of branching reticulating wrinkles pro- 

 ducing oblong or diamond-shaped pits. Umbo of posterior valve 

 central, but little projecting. 



Interior : Sutural plates well developed, the sinus deep, angular. 

 Anterior valve having 10-13, central valve 2-4, posterior valve 

 10-12 slits. 



Girdle having fine, close, solid imbricating scales. 



Length 75, breadth 30 mill. ; divergence about 130. 



Leifgth 55, breadth 27 mill. 



Monterey, California, south to Magdalena Bay; Catalina and, 

 Sta. Barbara Is. 



Chiton magdalenensis HINDS, Zool. Voy. 'Sulphur' ii, p. 54, t. 

 19, f. 1. REEVE, Conch. Icon. t. 5, f. 20b. Stenoradsia magdalen- 

 ensis CPR. S. "magdalensis" KEEP, West Coast Shells, p. 107, f. 

 94, and of collectors generally. 



This species differs from I. conspicuus in its pitted instead of finely 

 granulose central areas and in the mantle-covering of minute, solid 

 scales, unlike the short spines of the other form. It differs from /. 

 acrior in the much finer sculpture and more delicate coloring. 



