Vol. XI] BERRY— FOSSIL CHITONS 473 



27. Ischnochiton (Lepidozona) cooperi Carpenter, 1879 

 (Plate XL) 



1879. Iscluiochiton cooperi Carpenter, in Dall, Proc. U. S. Nat. 



Mus., v. 1, p. 296, pi. 2, f. 15 (radula). 

 1892. Ischnochiton (Ischnochiton) cooperi Pilsbry, Man. 



Conch., (1), v. 14, p. 127, pi. 26, f. 27-30. 

 1919. Ischnochiton cooperi Chace and Chace, Lorquinia, v. 2, 



p. 43 [3] (recorded from Pleistocene of Pt. Fermin, 



Cal.). 



Diagnosis: Valves moderately thin, strongly elevated, 

 sharply carinate ; side slopes straight or but weakly arcuate ; 

 lateral areas elevated, with 5-6 low radial flutings, each bear- 

 ing a series of usually elongate, often abraded pustules, the 

 posteriormost coarser and projecting backward so as to pecti- 

 nate the sutural margin ; head valve similarly sculptured, the 

 ribs 20-30 in number, their interspaces distinctly fluted out and 

 concentrically decussated by the lines of growth ; posterior 

 area of tail valve similar but with the lines of pustules rather 

 less definitely arranged ; central areas sculptured by about 20 

 very sharply cut, longitudinal ribs, straight at the sides but 

 distinctly diverging on the jugal tracts of all the valves, es- 

 pecially the second, their interspaces decussated by numerous, 

 very closely placed, transverse riblets of much less prominence ; 

 mucro of tail valve low, scarcely projecting, nearly median ; 

 sutural laminae low, wide, connected across the shallow sinus 

 by a dentate plate; teeth short, not projecting; eaves solid; 

 slits 8 to 11, 1-1, 9 to 11, with distinct pore lines leading into 

 them. 



Recorded Range: 



Pleistocene: Lower San Pedro Series — Chiton Bed, Point 

 Fermin, California (Chace and Chace, !) ; near lighthouse, 

 Point Fermin, California ( !) ; Nob Hill Cut, San Pedro, Cali- 

 fornia ( !) ; "Crawfish George's", San Pedro, California ( !). 



Formation doubtful — Deadman Island, San Pedro, Cali- 

 fornia ( ! ) . 



Living: Coos Bay, Oregon ( !) , to Anacapa Islands, Santa 

 Barbara Group, California (Yates). 



