1 26 ISCHNOCHITOX. 



cents of the same color. Sutural plates low ; sinus flat, angular, finely 

 toothed. Anterior valve having 10-11, central valves 1, posterior 

 valve 10 slits; teeth rather short and obtuse, and usually distinctly 

 roughened ; eaves rather wide. 



Girdle firm, compactly covered with regular, solid, oval, shining 

 scales, which are usually smooth, but frequently are superficially or 

 obsoletely striated (figs. 22, 23.) 



Length 35, breadth 21 mill. 



Length 38, breadth 23 mill. 



Sitka south to Monterey, California. 



Chiton mertensii MIDD., Bull. Acad. Sc. St. Petersb. vi, p. 118, 

 1846. Chiton (Phcenochiton, Hamachiton, Stenosemus) mertensii 

 MIDD., Mai. Ross., p. 34, 125, t. 14, f. 1-3, 1347.Leptochiton 

 mertensii H. & A. AD., Gen. Rec. Moll, i, p. 473, 1854. Lepido- 

 pleurus mertensii CPU., MS., and DALL, Proc. U. S. Nat. Mus. 1878, 

 p. 332. 



This species may be known by the more or less red coloring, the 

 shining convex oval scales of the girdle, which are usually almost 

 smooth, and by the strongly developed sculpture. Attention has 

 already been directed to the similarity of the Chcetopleura gemmea 

 of Cpr. (p. 31), which differs mainly in its sparsely hairy girdle. 



Southern examples of this species are larger and more frequently 

 variegated with white than those from the northern part of its 

 range; and the girdle scales seem to be more distinctly striated. 

 They seem to be almost or entirely smooth in most northern speci- 

 mens, as far as my material shows; and I do not doubt that Car- 

 penter's figure (pi. 26, fig. 23) was drawn from a specimen collected 

 north of San Francisco. In almost all of the specimens from the 

 south which I have examined, the scales show a delicate striation 

 when illuminated from the side, or at right angles to the direction 

 of the stria3. This is shown in figure 22, drawn by the author from 

 a Monterey specimen. The sculpture of the valves is peculiar: the 

 jugal area has diverging line, with smooth intervals. This is 

 always most pronounced on the second valve (fig. 24), the other 

 valves often having the lirse more nearly parallel, and the intervals 

 not all smooth. This is shown in fig. 25, representing a fourth 

 valve ; but in some specimens the divergence is even less pro- 

 nounced than in this. The pustules upon the front valve occas- 

 ionally become soldered together into riblets, but those of the tail 

 valve seem to remain distinct. 



