PROCEKDINGS 



OF THE 



CALIFORNIA ACADEMY OF SCIENCES 



Fourth Series 



Vol. IX, No. 1, pp. 1-36, pis. 1-8 June 16, 1919 



I 



NOTES ON WEST AMERICAN CHITONS— II. 



BY S. STILLMAN BERRY, REDLANDS, CALIFORNIA 



3. On the Generic or Subgeneric Position of Certain 

 West American Chitons 



Specimens now in hand of the two Australian species. 

 Ischnochiton australis (Sowerby) and /. novcBhollandice 

 Gray, make it evident that most of the species from other 

 regions which have been associated with them in the section 

 or subg-enus Ischnoradsia of Shuttleworth, of which the 

 former species must be taken as the type, have no true rela- 

 tions With them whatever. One of our West North Ameri- 

 can species which has clearly been incorrectly included here is 

 the aberrant Ischnochiton trifidus Carpenter, 1864. As this 

 species appears to have no close connection with any other 

 known to us, while it ofifers several rather remarkable features 

 of its own, I propose to make it the type of a new group, 

 Tripoplax, which for the time being may be tentatively re- 

 ferred to Ischnochiton as a subgenus. In the true Ischnorad- 

 sia, not only is the sculpture, especially that of the lateral and 

 terminal areas, of a different order, but the girdle scales are 

 relatively quite large, thick and heavy, and bear a conspicuous 

 vertical carination on their outer aspect. In the West Ameri- 

 can species the lateral and terminal areas have only a rela- 



June 16, 1919 



