Vol. IX] BERRY— NOTES ON WEST AMERICAN CHITONS 15 



tubercles of the diagonal rib and the riblets in front, the 

 innermost ones bending in abruptly behind toward the deep, 

 acute, A -shaped caudal sinus. 



Interior of anterior valve with the eight whitish radial 

 lines leading to the marginal slits very conspicuous, each 

 accompanied by a series of seven or eight transversely slit-like 

 pores in the overlying translucent articulamentum. Inter- 

 mediate valves with a slight transverse thickening across 

 the middle ; whitish lines radiating to the slits as in the 

 anterior valve, but the overlying pores 12 or more in number. 

 Posterior valve with 2-3 of the pores conspicuous below the 

 slits, but the white lines not visible, perhaps because of the 

 heavy, transverse, posterior callus; an oblique thickening also 

 extends forward on each side of the central depression lead- 

 ing to the sutural sinus. Teeth in all valves but the last 

 short, broad, squarish; insertion slits bounded on each side 

 by conspicuous tile-like upturnings of the edges of the teeth 

 and sutural laminae. Sutural laminae of intermediate valves 

 exceedingly thin and fragile, very broad, only slightly 

 arcuate in front, the sinus small and narrow; posterior valve 

 with proportionally rather longer, more sinuous laminae, the 

 narrow sinus sharply squared at the base; caudal sinus of 

 articulamentum about as in tegmentum but more rounded 

 at apex. 



Eaves short, thin, sharp; very slightly projecting over the 

 thin layer of coarsely spongy tissue beneath. Anterior valve 

 with 8, intermediate valves with 1-1, posterior valve with 1-1 

 slits. 



Girdle moderately wide, only slightly encroaching at the 

 sutures; sharply slit posteriorly; dorsal surface covered with 

 numerous very minute spines or scales, with larger dirk- 

 shaped spinelets at the margin; inner central portion devoid 

 of setae ; sutural setae conspicuous, long, erect, comprising each 

 a long, slender, curved, amber-colored bristle, from the basal 

 portion of which are given off on the upper side numerous 

 nearly straight, long slender, needle-like, whitish aciculae ; four 

 such setae around the head valve, one in the angle of the 

 first six sutures, one nearly halfway out on the girdle on 

 each side opposite the last suture, and one very strongly 

 tufted unpaired seta in the caudal sinus a little less than half 



