\-0L. IX] BBRRV— NOTES ON If EST AMERICAN CHITONS 19 



sulcus narrow, but distinct ; each rib ornamented by two or 

 sometimes only one series of small, easily abraded pustules 

 similar to those of the anterior valve, 2-5 in a series ; central 

 areas on each side sharply and finely sculptured with 15-18 

 narrow, minutely granulose. longitudinal riblets, finely inter- 

 latticed between so as to resemble knitted work ; jugal tract 

 usually devoid of distinct ribbing or other sculpturing except 

 the scaly granulation already noted, though sometimes a con- 

 tinuation of the pleural sculpturing is evident extending to 

 the ridge as a more or less obsolete, irregular reticulum. 



Posterior valve with mucro well in front of the middle, 

 and the posterior slope nearly straight ; region behind mucro 

 with sculpture similar in nature to that of the anterior valve, 

 but in every way weaker and sometimes nearly obsolete; 

 region in front sculptured like the central areas of the inter- 

 mediate valves. 



Articulamentum transparent, hyaline, that of the inter- 

 mediate valves somewhat thickened across the middle. 

 Sutural lamin?e thin, sharp-edged, broadly arcuate, connected 

 across the sinus by a short, very delicate, weakly and rather 

 irregularly dentate plate, apparently surmounted by an ex- 

 tremely thin, delicate, anteriorly projecting rounded process 

 of the tegmentum forming a sort of "false beak". Insertion 

 teeth sharp, distinct, their edges perhaps sometimes very 

 weakly crenulate. Eaves thin, more or less fluted, rather pro- 

 jecting, but shorter than the teeth. In a dissected specimen 

 anterior valve with 9, intermediate valves with 1-1, posterior 

 valve with 12 slits. 



Girdle very delicate and fragile in dried specimens ; mod- 

 erately wide ; covered dorsally with a rather irregularly 

 imbricating armature of delicately ribbed-striate, convex 

 scales, rather small, but not proportionally to the size of the 

 shell, the ribs about 8-11 in number on each scale. 



Color of outer surface of shell a yellowish brown, under 

 a lens seen to be more or less mottled with a deeper tone. 

 Girdle usually maculated above by alternating bands of 

 brown and tan, corresponding respectively in position with 

 the sutures and valves. Interior of shell hyaline or slightly 

 porcellanous, underlain with white, and with the gray or 

 brown of the tegmentum showing through. 



