Vol. XI] BERRY— FOSSIL CHITONS 475 



28. Ischnochiton (Lepidozona) mertensii ( Middendorff, 1846) 

 (Plate X, figs. 7-12.) 



1846. Chiton Mertensii Middendorff, Bull. Acad. Sci. St. 



Petersb., VI, p. 118 (fide Pilsbry). 



1847. Chiton {Phoenochiton, Hamachiton, Stenosemus) Mer- 



tensii Middendorff, Malac. Ross., p. 34. 125, pi. 14. 



f. 1-3. 

 1879. Lepidopleurus Mertensii Dall. Proc. U. S. Nat. Mus., v. 



1. pp. 297. 332, pi. 2. f. 18-18a (radula). 

 1802. Ischnochiton (Ischnochiton) mertensii Pilsbry. Man. 



Conch.. (1). v. 14, p. 125, pi. 26. f. 20-26. 



Diagnosis": Valves moderately thin, fairly elevated, cari- 

 nate ; side slopes straight or but weakly arcuate ; lateral areas 

 elevated, divided by shallow, narrow grooves into 5 or 6 low, 

 often obscure, flattened, radial ribs, each bearing a series (some- 

 times bifurcating) of rounded or pyriform pustules, the poster- 

 iormost series directed obliquely backward so as to dentate the 

 suture: head valve similarly sculptured, the ribs and grooves 

 perhaps 25 in number; posterior area of tail valve-similar; cen- 

 tral areas sculptured by 12-15 sharply cut longitudinal bars. 

 subparallel on the pleural regions but usually distinctly di- 

 vergent on the jugal tracts, especially on valve ii, their inter- 

 spaces, except as a rule on the jugum, decussated by numerous 

 radially arcuate, transverse riblets of much less prominence; 

 mucro of tail valve low, median; sutural plates low, wide, con- 

 nected across the sinus by a dentate plate ; teeth short, not pr< >- 

 jecting; eaves solid; slits 10 to 11, 1-1, 10 to 12. 



Recorded Range: 



Pleistocene (?): Formation doubtful — Deadman Island, 

 San Pedro, California ( !). 



Living: Sitka, Alaska (Dall). to San Martin Island, 

 Lower California (Baker) ; between tides to 50 fathoms. 



18 Description drawn in part from recent specimens. 



