Vol. VII] 



BERRY— WEST AMERICAN CHITONS 



237 



arated, distinct, rounded pustules. Median valves : lateral areas 

 distinctly raised, sculptured like the anterior valve, but the 

 5 to 7 ribs relatively wider and more flattened, the defining 



Fig. 1. Ischnochiton (Lepidozona) willetti Berry, camera outline 

 of dorsal aspect of type specimen, xlj4. 



grooves sometimes, but not always, sharply chiseled (fig. 2) ; 

 central areas on each side sharply sculptured with 20-25 nar- 

 row, faintly beaded, longitudinal ridges, their interstices trav- 

 ersed by low, rather irregular cross-ridges, becoming nearly or 

 quite obsolete at the jugum. Posterior valve with mucro well in 

 front of center; region behind mucro sculptured like the an- 

 terior valve, but the 28-30 ribs rather less distinct and the 



Fig. 2. Ischnochiton {Lepidozona) willetti Berry, sketch of 



portion of 5th valve of type to indicate the general 



scheme of sculpturing, x8. 



grooves less conspicuous ; region in front of mucro sculptured 

 like the central areas of the intermediate valves. 



Interior of central valves thickened across the middle. Teeth 

 with a distinct fossa separating them at base from body of 



