ARNOLD — THE PALEONTOLOGY AND STRATIGRAPHY OF SAN PEDRO. 343 



One valve was found in the lower San Pedro series of Deadman Island, and 

 two in the Pliocene of the same locality. One is probably an end valve and is 

 distinguishable by its strong convexity, thickness, and smooth surface. It has a 

 .small, acute notch on each side near the end. 



Dimensions. — Long. 20 mm.; lat. 30 mm.; alt. 13 mm. 



Living. — Straits of Fuca to Monterey; Kamtschatka (Cooper): Hakodate, 

 Japan (?) (Carpenter). 



Pleistocene. — San Diego (Cooper): San Pedro (Arnold). 



Pliocene. — Deadman Island, San Pedro (Arnold). 



Superfamily OPSICHITONIA. 

 Family LXXXIX. MOPALIID^. 



Genus Mopalia (rraij. 



Shell regular; laminae lengthened; anterior valve with six or more slits, the others with a 

 single slit; last valve sinulate behind; sinus narrow, mucro median, depressed; sutures indented; 

 girdle wide, bristly, sometimes fissured behind, sometimes projecting anteriorly. 



Mopalia hlainvillei Brod. is a characteristic species. 



405. Mopalia ciliata Soiverby. 



Chiton muscosus Gld., Proc. Best. Soc. Nat. Hist., Vol. II, 1846, p. 145; Wilkes' Expl. Exped., 



Vol. XII, p. 313, fig. 436, 1852. 

 Mopalia muscosa Gld., Cpr. , Brit. Assn. Rept., 1863, p. 648. 

 Mopalia ciliata Sby., Keep, West Coast Shells, p. no, fig. 98, 1892. Williamson, Proc. U. S. 



Nat. Mus., Vol. XV, 1892, p. 196. 



Shell depressed, rather broad, oval; obliquely ridged along the back; sculpture prominent 

 and covering whole of surface; side areas sculptured with granulated, radiating ridges; central area 

 ornamented with longitudinal, granulated, raised lines; mucro median depressed, ornamented with 

 sharp, oblique lines which meet on middle and form an acute angle open anteriorly; anterior valve 

 large, semicircular, with ten granulated, elevated, radiating lines, and interspaces granulated as in 

 lateral areas. 



Dimensions. — Long. 40 mm.; lat. ig mm.; depth 6 mm. 



Description from living specimen. The only specimen of this species ever 

 reported in the fo.ssii state was found in the upper San Pedro series of San Pedro. 

 It is a perfect anterior valve, 10 millimeters wide and 5.2 millimeters long. 



Living. — Vancouver to Monterey (Carpenter): San Pedro (Williamson). 



Pleistocene. — San Pedro (Arnold). 



