Animal rather small to moderate in size, varyingly broadly ovate in outline; low-arched, with straight slopes, the jugum acute. Valves beaked when unworn. Entire tegmental surface covered with numerous low, crowded but microscopically discrete, rounded granules, without evident linear alignment on the terminal and lateral areas, but showing on the central areas a tendency to arrange themselves in longitudinal lines, with sometimes more or less of a quincuncial effect toward the jugum. Lateral areas only slightly raised, but in the best specimens fairly well defined and showing a slight tendency to form a rib on the diagonal. Mucro of posterior valve nearly median.
Sutural laminae short and broad, separated by a shallow sinus which is quite wide on most of the valves. Teeth very short, the eaves very thin and short, their texture microscopically porous. Slit formula 10 or 11, 1-1, 13 to 16.
Girdle rather narrow, clothed above with small, closely packed, granular scales, giving it a characteristic gritty look. Color gray, drab, brown, olivaceous, or, rarely, cream, usually very finely mottled with dark brown or slate, and often with a few alternating light and dark sutural spots. Rather uncommonly the markings occur in a more conspicuous pattern. The girdle is commonly clouded with alternating patches of light and dark, more or less approximating the colors of the tegmentum.
Dimensions: of holotype, max. long. 14.0, max. lat. 9.0, long, shell only 12.9, lat. tegmentum valve v 7.4, alt. 3.5 mm.
Holotype: Cat. No. 11992 Berry Collection [2146].
Type Locality: Newport Bay, Orange County, California; Emery P. Chace.
Remarks: This is one of the most abundant and best known intertidal chitons of southern California, and it is indeed curious that it has so long escaped a good title to a name. Under the erroneous name dentiens it has several times been figured, e.g. by Pilsbry (1892:73, 74, 335, pi. 8, figs. 61-65) and, in the fossil state, by Berry (1922:438, pi. 1, figs. 7-9). It is associated with no very close relatives in our waters, the nearest probably being the various species of Cyanoplax and Tonicella. On geographic grounds its reference to Lepidochitona does not appear to be too happy, although at the present time it is difficult to suggest a better association for it. Some very pretty and often bizarre colorforms occur.