342 CALIFORNIA ACADEMY OF SCIENCES. 



Subclass ISOPLEURA. 



Order POLYPLACOPHORA. 



Superfamily EOCHITONIA. 



Family LXXXVIII. CHITONID.E. 



Genus Ischnochiton Gray. 



Shell thin; laminffi of insertion regular, acute, neither pectinate nor serrate; eaves large; 

 sinus usually smooth; girdle squamose, the squama; generally striate. 



Ischnochiton longicymoa Blainv. is a characteristic species. 



403. Ischnochiton regularis Carpenter. 



Chiton regularis Cpr., Proc. Zool. Soc, 1855, p. 232. 



hchnochiton regularis Cpr., Keep, West Coast Shells, p. 107, fig. 93, 1892. Tryon, Man. Conch., 

 Vol. XJV, p. 142, PI. XVIII, figs. 41, 46, 1892. 



Shell depressed, elongate-oval, width half of length; valves not sharply arched; lateral areas 

 ornamented with concentric, slightly granular ridges and fine radiating lines; central area with 

 inconspicuous fine irregular lines; apex smooth; mucro longitudinally ridged with irregular raised lines. 



Description partly from living shell. The only fossil rejjresentative of this 

 sjjecies so far reported is a perfect central valve found in the upper San Pedro series 

 of San Peih-o in 1894 by Dr. G. H. Ashley. 



Living. — Monterey (Carpenter): West Coast (Keep). 



Pleistocene. — San Pedro (Ashley). 



Genus Gryptochiton Mldd. d- Gray. 

 Shell large; valve entirely immersed in the girdle, which is minutely fasciculately pilose. 

 Type, Cryptochiton stelleri Midd. 



404. Gryptochiton stelleri Mkidendorff. 



Chiton stelleri Miuu., Bull. Acad. St. Peters., Vol. VI, 1S46, p. 116. 



Chiton (yCryptochitori) stelleri M\t>d., Mai. Ross., Pt. i, p. 93, PI. I, figs, i, 2, 1847. 



Chiton amiciilatus S^\., Thes. Conch., Ill, Chitons, fig. 80. 



Chiton sitkensis RvE., Icon. Conch., PI. X, sp. 55. 



CryptochiloH stelleri Midd., Cpr., Brit. Assn. Rept. , 1863, p. 648. Gabb, Pal. Cal., Vol. 11, p. 87, 



1869. Tryon, Struct, and Syst. Conch., Vol. II, p 346, PI. LXXXV, fig. 83, 1883. 



Cooper, 7th Ann. Rept. Cal. St. Min., 18S8, p. 237. Keep, West Coast Shells, p. in, 



fig- 99, 1892. Tryon, Man. Conch., Vol. XV, p. 148, PI. VII, figs. 7-13; PL VI, 



fig. 6, 1893. 

 Chiton calif orniais Prescott, Am. Jour. Sci., 2nd Ser., Vol. XXXVIII, 1864, p. 185. 



