NO. 2223. CHITONS FROM THE NORTHWEST PACIFIC— BERRY. 11 



region to the posterior slits, the concavity of the mucro forming the 

 base of a low V-shaped callus extending forward; insertion teeth 

 irregularly roughened at margin (pi. 7, figs 2, 5). 



Anterior valve of paratype with 13 slits; intermediate valves with 

 2-2, 1-1, 1-1, 1-2, 2-2, 2-2 slits; posterior valve with 13 shts. 



Entire surface of shell rather closely, heavily granulose. Anterior 

 valve ornamented with many narrow radiating ribs, their total 

 number about 55 at the margin, but becoming fewer and fuially 

 almost obsolete toward the apex, said ribs for the most part broken 

 into a close set series of perhaps 20 low, distinct, rounded pus- 

 tules, the latter often somewhat worn, and the posterior series larger 

 and fewer (about 12) but so nearly obsolete as barely to dentate 

 the margin; interspaces shallow and ungrooved. Intermediate 

 valves with lateral areas slightly elevated and sculptured as above, 

 the pustulose ribs 5-7 in number, and with a series of some 7-10 

 larger, but more obsolete, pustules bordering the posterior margin ; 

 central areas with 20 (valve 7) to 26 (valve 4) pustulose riblets on 

 each side, usually a little narrower than their interspaces, the pustules 

 small but distinct and coinciding with the lines of growth so as to 

 appear grouped in squares, though usually the transverse connecting 

 ridges are very faint if present at all ; both ribs and pustules obsolete 

 over the jugal tract. Posterior valve ^^^th posterior and central 

 areas sharply delimited, the mucro forming an obtuse angle in their 

 boundary; sculpture as above, the posterior area with 30-35 radiating 

 pustulose ribs similar to those of the lateral areas (pi. 6, fig. 7). 



Girdle ^^^de, averaging about one-fourth the width of the median 

 valves. Dorsal scales translucent, rather small, crowded, closely 

 imbricate (pi. 6, fig. 8), their convex surfaces very finely ribbed- 

 striate, the numerous (12-18) riblets being so delicate that the scales 

 appear smooth under low magnifications (pi. 6, fig 9; pi. 7, fig. 6). 

 Marginal scales small, partly needle-like, partly robust spiniform, 

 the latter finely striate (pi. 7, fig. 6). 



Color of shell in alcohol a light tan with scattered dark red-brown 

 spots on the central areas and more numerously along the jugum, 

 where they blend to form conspicuous triangular maculations. 

 Girdle tan above, but darker and duller in tone than the groundwork 

 of the shell and very indistinctly mottled with brown. Ventral 

 surface of animal and girdle a fight tan. Interior of shell a pale 

 flesh color, some of the valves showing a narrow brownish ray on 

 each side of the jugum. 



The radula has strongly bicuspid major laterals, minutely winged 

 minor laterals, and fan-shaped rhachidian teeth (pi. 7, fig. 7). 



Ctenidia about 30 on each side, extending forward to the second 

 valve. 



