454 



CALIFORNIA ACADEMY OF SCIENCES 



[Proc. 4th Ser. 



with 8 slits, but in adult very imperfectly and irregularly de- 

 veloped, with numerous secondary slits ; median valves with 

 short but well projecting teeth and very wide sutural laminae, 

 continuous across the narrow, abrupt sinus ; tail valve with a 

 single pair of nearly obsolete lateral slits, rugose insertion 

 plates, and weak or nearly obsolete, posterior sinus ; mucro 

 posterior; eaves spongy; slits 8+, 1-1, 1-1. 



Recorded Range: 



Pleistocene: Lower San Pedro Series — Chiton Bed, 

 Point Fermin, California (Chace and Chace, !) ; near light- 

 house, Point Fermin, California (!). 



Formation doubtful — Deadman Island, San Pedro, 

 California (!). 



Living: Forrester Island, Alaska (!), to Todos Santos 

 Bay, Lower California ( !) ; between tides to 50 fathoms. 



Material Examined: 



^ 



Valve 



Locality 



Collector 



Where Deposited 



Formation 



Period 



Int. 

 Ant. 

 Int. . 



Int. . 



Chiton Bed, Pt. Fermin, Cal . 

 Chiton Bed, Pt. Fermin, Cal . 

 Near lighthouse, Pt. Fermin 



Cal 



Deadman Id., San Pedro, Cal . 



E. P. & E. M. Chace, 1918 

 E. P. Chace, 1920 



E. P. & E. M. Chace, 1918 

 Arnold Coll 



Berry Coll. Cat. 4106. 

 Berry Coll. Cat. 4106. 



Berry Coll. Cat. 4110. 

 Dept. Geology, 

 Stanford Univ 



[1092] 

 [1358] 



[HOI] 



[ 677] 



Lower San Pedro. 

 Lower San Pedro. 



Lower San Pedro. 

 ? 



Pleistocene 

 Pleistocene 



Pleistocene 

 ? Pleistocene 



Remarks: A valve in the Arnold collection from one of 

 the Deadman Island formations is apparently referable to the 

 bizarre P. velata, although it seems more than usually short 

 and broad even for this species. Though somewhat chipped 

 and worn it is on the whole in a very fair state of preserva- 

 tion, and is here figured. That the specimen is a second valve 

 is indicated by the anteriorly projecting angle of the teg- 

 mentum and the very oblique insertion slits. It has the follow- 

 ing caliper measurements : long. 7.0, diam. 26.7, alt. 8.4 mm. 



Three valves, mainly fragmentary, from the Point Fermin 

 exposures are the only additional fossil specimens which have 

 been seen. 



