342 CALIFOKNIA ACADEMY OF SCIENCES. 



Subclass ISOPLEURA. 



Order POLYPLACOPIIORA. 



Superfamily EOCHITONIA. 



Family LXXXVIII. CIIITONID.E. 



Genus Ischnochiton Gray. 



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

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



Ischnochiton longicymoa Blainv. is a characteristic species. 



403. Ischnochiton regularis Carpenter. 



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



Ischnochiton regularis CpR., Keep, West Coast Shells, p. 107, fig. 93, 1S92. Tryon, Man. Conch., 

 Vol. XIV, p. 142, PI. XVIIl, 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 rejiresentative of this 

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

 of San Pedro in 1894 by Dr. G. H. Ashley. 



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



Pleistocene. — San Pedro (Ashley). 



Genus Gryptochiton Midd. <£• Graij. 

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

 Type, Cryptochiton steUeri Midd. 



404. Cryptochiton stelleri Middendorf. 



Chiton stet/eri M IDT)., Bull. Acad. St. Peters., Vol. VI, 1S46, p. 116. 



Chiton (Cryptochiton) stelleri MiDD., Mai. Ross., Pt. i, p. 93, PI. I, figs, i, 2, 1847. 



Chiton amiculalus S]i\'., Thes. Conch., Ill, Chitons, fig. 80. 



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



Cryptochiton stelleri Midd., Cpr., Brit. Assn. Rept., 1863, p. 648. Gaiu!, Pal. Cal., Vol. II, |). 87, 



1869. Tryon, Struct, and Syst. Conch., Vol. II, p 346, PI. LXXXV, fig. 85, 1883. 



Cooper, 7th Ann. Rept. Cal. St. Min., 1888, p. 237. Keep, West Coast Shells, p. 1 1 1, 



fig- 99. 1892. Tryon, Man. Conch., Vol. X\', p. 148, PI. VII, figs. 7-13; PI. VI, 



fig. 6, 1893. 

 Chiton calif amicus Prescott, Am. Jonr. Sci., 2nd Ser., Vol. XXXVIII, 1864, p. 185. 



