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
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