470 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



1879. Ischnochiton regularis Dall, Proc. U. S. Nat. Mtis., v. 



1, p. 296, pi. 2, f. 14 (radula). 

 1893. Ischnochiton regularis Pilsbry, Man. Conch., (1), v. 14, 



p. 142, pi. 18, f. 41-46. 

 1895. Ischnochiton regularis Ashley, Proc. Cal. Acad. Set. 



(2), v. 5, p. 343 (recorded from Pliocene of San 



Pedro). 

 1903. Ischnochiton regularis Arnold, Mem. Cal. Acad. Sci., v. 



3, p. 28, 42, 85, 342 (recorded from Pleistocene of 



San Pedro, Cal.). 

 1906. Ischnochiton regularis Arnold, Pectens of Calif., p. 35 



(recorded from Pleistocene of San Pedro, Cal.). 

 1910. Callisto chiton regularis Thiele, Rev. Syst. Chit., IT, 



p. 112, 113. 

 1919. Ischnochiton (Rhombochiton) regularis Berry, Proc. 



Cal. Acad. Sci., (4), v. 9, p. 2. 



Diagnosis 16 : Valves thin, elevated, carinate, not beaked; 

 side slopes nearly straight; lateral areas only slightly raised, 

 these and the terminal areas very delicately radially threaded : 

 central areas with numerous, very fine and regular, micro- 

 scopically granose riblets ; mucro in front of middle of tail 

 valve ; insertion plates low and wide, connected across the sinus 

 by a delicately toothed plate; teeth sharp; eaves solid; slits 14 

 to 16, 2-3, 22. 



Recorded Range: 



Pleistocene: Upper San Pedro Series — Lumber yard. San 

 Pedro, California (Arnold). 



Formation Doubtful — San Pedro, California (Ashley). 

 Living: Fort Bragg, California ( !), to San Diego, Cali- 

 fornia (Kelsey) ; between tides. 



Remarks: Besides the old record of Ashley, this species has 

 been reported from the type locality of the Upper San Pedro 

 Series at San Pedro by Arnold, but I have been unsuccessful 



16 Description drawn from recent speciinens. 



