12 THE NAUTILUS. 



3. Vauatta, E, S. "Rafiiiesque Type of Unio, " Proc. Acad. 



Nat. Sciences, Philadelphia, 1916. 



4. Sterki, V. "A Preliminary Catalo^e of the Land and 



Freshwater Mollusca of Ohio." Proc. Ohio Acad. Sci- 

 ence, IV, pt. 8. 



A FURTHER NOTE ON THE OENUS TRACH7DERM0N. 



BY S. STILLMAN BERRY, REDL.iNDS, CALIFORNIA. 



Since the publication of my note on the chiton genus Tra- 

 (hydermon in the Proceedings of the California Academy of 

 Sciences, (4), vol. 7, p. 245, September, 1917, Mr. Tom Ire- 

 dale has supplied me with the interesting information that 

 Tnichydernw-n Carpenter 1864 is preoccupied, and hence can- 

 not be used in Polypkicophora in any sense. Tliis consider- 

 ably clarifies the whole situation by rendering needless any 

 further investigation as to which species is properly to be re- 

 garded as the type of the genus. At the same time the pecu- 

 liar group of West American chitons comprising the old Tra- 

 chydermmi flectcns Carpenter and the remarkable Mopalia 

 heathii of Pilsbry is automatically left without a name. Hav- 

 ing ascertained from Mr. Iredale that he is chiefly concerned 

 with certain other consequences of the nomenclatural tangle 

 we have discussed and has, himself, no intention of taking up 

 the present question, I feel at liberty to propose the new 

 generic name, BasUiochiton, based upon Mopalia heathii Pils- 

 bry 1898 as its typical representative. A cogent argument for 

 the selection of this rather than the older species as the type 

 of tlie genus is that the whereabouts, if not the very existence, 

 of the type specimen of Carpenter's flectens appears to be 

 unknown. I had supposed it to be in the British Museum, 

 but Mr. Iredale writes me that it is not there. It is possible 

 that it was destroyed along with so many other Carpenterian 

 specimens in the San Francisco conflagration of 1906. 



A further and fuller discussion of this group of chitons will 

 appear in a forthcoming publication. 



