Vol. VII] BERRY— WEST AMERICAN CHITONS 239 



14. Trachydermon flectens (Carpenter) 



One specimen of this species was taken at low tide inside 

 Cape Lookout, Dall Island. Others were dredged at Forrester 

 Island in 15-30 fathoms. 



My reasons for the unusual position in which I have placed 

 Trachydermon in the list will be given in the next note of this 

 series. 



15. Mopalia ciliata (Sowerby) 



Four specimens more or less referable to typical ciliata as 

 redefined by Pilsbry were taken in 15 fathoms at Forrester 

 Island [S. S. B. 278]. 



The last word has not been said on the West American 

 Mopaliae, and I have no hope that my treatment of them here, 

 merely adapted as it is from work done a considerable period 

 ago, can be more than provisional. This remark is not to be 

 construed as an attempt to carp at the older w'ork. That of 

 Pilsbry in particular constituted a tremendous advance in our 

 understanding of the entire group and stands alone not only as 

 a reference work, but as a priceless text and source of inspira- 

 tion to every subsequent student of Polyplacophora. But dried 

 specimens, upon which most taxonomic work in this group has 

 perforce been done, are often extremely deceptive, and this is 

 notoriously the case with the Mopalias. In this instance it is 

 going to require a far more extensive array of well-preserved 

 alcoholic material than exists at present, I fear, in all our col- 

 lections, to definitely settle the status of the numerous named 

 forms, let alone the many others which still remain to be de- 

 scribed. No doubt Dall and Pilsbry have generally been quite 

 correct in reducing many of the earlier species to synonymy, 

 but I feel certain that in some cases the process has been carried 

 too far. 



Some of Mr. Willett's small Mopalias form a curious as- 

 semblage, but the series is not sufficiently complete and the 

 proportion of specimens preserved in alcohol too scanty to 

 permit the drawing of satisfactory conclusions from them at the 

 present time, though I think it apparent that not all are to be 

 regarded as young stages of the older species. The Mopaliid?e 

 are never an easy group, but the difficulty of dealing with them 



