Vol. VII] BERRY— WEST AMERICAN CHITONS 233 



mixture. The relatively delicate and smooth-shelled Lepido- 

 pleuridcB of the west American coast seem only diffidently 

 congeneric with L. cajetanus Poli, the thick rugose shell se- 

 lected by Pilsbry as Risso's type. It may be that further 

 anatomical work will require the dismemberment even of 

 Leptochiton, but in the meanwhile it does not seem to strain 

 the relationships seriously to make this genus do duty again. 



2. Leptochiton, species 



Numerous specimens of a worn Leptochiton, recalling the 

 southern L. rugatus, were taken "at pretty low tides" at the 

 Waterfall Cannery, Prince of Wales Island. One specimen 

 of the same was also taken at Cape Lookout, Dall Island. It 

 occurs under rocks. Whether the specimens are really ruga- 

 tus or some undescribed form must be determined by fur- 

 ther study. They differ from southern California (La Jolla) 

 specimens of rugatus in their much smaller size, whiter color- 

 ation, more pilose girdle and flatter posterior valve, only 

 slightly if at all concave behind the mucro. 



3. Tonicella ruber (Linnaeus) 



Taken at Forrester Island in 15-30 fathoms, occurring in 

 association with the small Tonicella I have here taken to be 

 young lineata (Wood). 



Balch ( :06, p. 62) has remarked at length upon the ap- 

 parent close relationship of this species and Tonicella mar- 

 morea. Ruber had for years been placed by nearly all writers 

 in Trachydermon, and to avoid separating the two generic- 

 ally, Balch thereupon removed mannorea to Trachydermon, 

 leaving the genus Tonicella to whatever might be its fate 

 after the loss of its type species. For reasons which will 

 presently be given in another connection, I have come to the 

 conclusion that Trachydermon is quite a different group from 

 what has generally been understood, but since both Sykes 

 ('94, p. 36) and Thiele ( :10, p. 107) have shown cause for 

 referring ruber itself to Tonicella, there is a convenient way 

 out of the difficulty. 



