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



Material Examined : 



Remarks: It is not without a little hesitation that I refer all 

 the specimens catalogued above to /. mertensii, as few of them 

 are sufficiently well preserved to be characteristic in all partic- 

 ulars. Several of them, e. g. 725, I think are almost certainly 

 this species, but the others are more doubtful. It may be that 

 there is another species represented in the lot, but -if so I do not 

 think it can be one of the known recent species. 



So far as shell characters go, the special features of mertensii 

 are the numerous, usually distinctly separate, rounded or pear- 

 shaped pustules of the terminal and lateral areas, the relative 

 coarseness of the latticing between the longitudinal ribs of the 

 central areas, and the fact that these ribs usually diverge 

 strongly on the jugal tract of all the valves, except of course 

 the head valve, their interspaces in this region being smooth 

 as a rule, or with only weak traces of the interlatticing. 



Although recorded from as far south as Lower California, 

 this species cannot be said to be a common one much below 

 Monterey County, and its presence in any numbers in any 

 horizon to that extent would therefore indicate northern affini- 

 ties. In southern California at the present time its place 

 between tides is everywhere taken by /. pectinulatus, mertensii 

 here being an off-shore species. 



29. Ischnochiton (Lepidozona) cf. sinudentatus 



Carpenter, 1892 



(Plate XII, figs. 10-17) 



?1892. Ischnochiton (Ischnochiton) sinudentatus Carpenter, 

 in Pilsbry, Man. Conch., (1), v. 14, p. 128. 

 Recorded Range: 



