Vol. XII BERRY— FOSSIL CHITOXS 453 



Section Stenoradsia Carpenter, 1879 



22. Ischnochiton (Stenoplax) magdalenensis (Hinds, 1844) 



(Plate VII, figs. 4-10.) 



1844. Chiton magdalenensis Hinds, Zool. Voy. "Sulphur", v. 



2, p. 54, pi. 19, f. 1. 

 1864. Ischnochiton Magdalcnsis Carpenter, Rep. Brit. Assoc. 



Adv. Sci., 1863, pp. 621, 649, 665. 

 1879. Stenoradsia magdalenensisDa.il, Proc. U. S. Nat. Mus., 



v. 1, p. 296, 330, pi. 2, f. 12 (radula). 

 1888. Ischnochiton magdalcnsis Cooper, 7th Ann. Rep. Cal. 



State Miner., p. 244 (recorded from Quaternary of 



Santa Barbara, Cal.). 

 1892. Ischnochiton (Stenoplax) magdalenensis Pilsbry, Man. 



Conch., (1), v. 14. p. 62, pi. 15, f. 98-100. 

 1919. Ischnochiton magdalenensis Chace and Chace, Lorquinia, 



v. 2, p. 43 [3] (recorded from Pleistocene of Pt. 



Fermin, California). 



Diagnosis: Valves of moderate thickness, depressed, sub- 

 carinate, all but the tail valve more or less concave behind, not 

 beaked; lateral areas strongly elevated, these and the terminal 

 areas ornamented by numerous fine ribs separated by rather 

 sharp grooves, and interrupted to some extent by some of the 

 lines of growth, yet not so conspicuously terraced as in /. falla.v; 

 central areas, where unworn, sculptured by numerous very fine 

 anastomosing axial wrinkles, becoming more or less reticulated 

 and pitted on the sides ; slope of head valve straight or very 

 weakly concave ; tail valve large, with weakly projecting, cen- 

 tral mucro : sutural lamin?e long, triangular, slightly sinuous, 

 with steep inner slopes; sinus wide, deep, notched at each side; 

 teeth well developed, but surpassed by the projecting, solid 

 eaves ; slits 10 to 13, 2 to 4, 10 to 12. 



Recorded Range: 



Pleistocene: Lower San Pedro Series — Chiton Bed, Point 

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

 Point Fermin, California ( !). 



Formation doubtful — S anta Barbara, California 

 (Cooper) ; Deadman Island, San Pedro, California ( !). 



