NUTTALLINA. 281 



forward and laterally upon the sutural plates ; the median ridge 

 and sulci more or less obsolete. Tail valve shorter, with less pos- 

 terior mucro. Color of valves lighter, more variegated. 



Girdle rusty brown or alternately blackish and white ; bearing 

 rather sparsely scattered white spike-like spines, sometimes having 

 one or two at each suture. (PL 54, fig. 21). Length 29, breadth 

 13 mill. 



Santa Barbara Is. and San Diego to between Scammon's Lagoon 

 and Pta. de Abreojos, Lower California. 



Chiton seaber REEVE, Conch. Icon., t. 17, f. 106 (March, 1847). 

 Acanthopleura fluxa CPU., Suppl. Rep. Brit. Asso. 1863, p. 649 ; 

 Proc. Cal. Acad. iii, p. 211, (1865.) 



This species has hitherto been confused with the preceding by 

 most collectors. Carpenter, however, distinguished it, and gave the 

 name fluxa. Although the individual valves are much shorter in 

 this species than in N. californica, they overlap much less, so that 

 the total length of the animal is about the same in the two species. 

 The elevation is about equal also, but in californica the girdle is 

 generally wider at the sides, especially in old specimens. In size, 

 individuals of the northern species considerably exceed any of the 

 southern I have seen, although the majority of specimens do not 

 differ much. 



N. ALTERNATA Sowerby. PI. 54, figs. 25, 26, 27. 



Shell elongated, subdepressed, very minutely granulated ; lightly 

 keeled by a central rib ; lateral areas separated by a lateral rib. 

 Anterior valve radiately ribbed ; posterior valve small. 



Girdle furnished with minute spines, alternately banded black 

 and white. Length 15, breadth 8? mill. 



Narrow, rather flat, minutely granulated; the first valve radiated 

 with slightly raised ribs, the intermediate have each three faint 

 ribs, one dorsal, the other two lateral ; the last is very small, with 

 a nearly terminal apex. The margin is covered with very minute 

 spines, in alternate patches of black and white ; general color, dark 

 olive-green. (Sowb.) 



Japan (Mus. Cuming). 



Chiton alternatus SOWB., Mag. of Nat. Hist., 1840, p. 288 ; Conch. 

 Illustr., f. 141. 



