318 CALIFORNIA ACADEMY OF SCIENCES. 



359. Acmaea insessa IIin(h. 



Patella hisfssa Hds., Ann. & Mag. Nat. Hist.. Vol. X, i860, p. 82, PI. VI, fig. 3. 



Nacella incessa Hns., Cpr., Brit. Assn. Rept., 1863, p. 650. Garb, Pal. Cal., Vol. II, !>. S7, 1869. 



Cooi'ER, 7th Ann. Rept. Cal. St. Min., 1888, p. 227. Keep, West Coast Shells, p. 103, 



fig. 91, 1892. 

 Acnitra insessa Hds., Dall, Am. Jour. Conch., Vol. VI, 1871, p. 244, Pi. XIV, fig. 3. Tryon, 



Man. Conch., Vol. XIII, p. 18, PI. VI, figs. 36, 37, i8gi. Williamson, Proc. U. S. 



Nat. Mus., Vol. XV, 1892, p. 197. 



Shell limpet-shaped, rather thick, brown; apex acute and dark, with light band around dark 

 spot (this coloration due to the wearing of shell through outer layer); sculpture consists of fine incre- 

 mental stria-; margin inclined to be compressed as the shell grows old; ape.x slightly anterior. 



Dimensions. — Long. 17 mm.; lat. 10 mm.; alt. ii mm. 



Found in tlie Pliocene of Deadman rslniid; the lower San Pedro series of 

 Deadraan Island and San Pedro; and the upper San Pedro series of Deadman 

 Island, San Pedro, Los Cerritos, and Crawfish George's. Found in the Plei.stocene 

 at bath-house, Santa Barbara; and at Spanish Bight, San Diego. 



Living. — Sitka to San Diego (Dall). 



Pleistocene. — San Diego (Cooper): San Pedro; Santa Barbara; San Diego 

 (Arnold). 



Pliocene. — San Pedro (Arnold). 



360. Acmaea instabilis Gould. 



Patella instabilis Gld., Proc. Bost. Soc. Nat. Hist., Vol. II, 1846, p. 150. 



Nacella insladilis Old., Cpr., Brit. Assn. Rept., 1863, p. 650. Keep, West Coast Shells, p. 103, 



1892. 

 Acmtea insladilis Gld., Dall, Am. Jour. Conch., Vol. VI, 1871, p. 245. Tryon, Man. Conch., 



Vol. XIII, p. 18, PI. VI, figs. 32, 33, 1891. Cooper, Bull. No. 4, Cal. St. Min. Bureau, 



Part III, 1894, p. 24. 



Shell resembles A. insessa, but is much larger when adult; apex rounded; sculpture con- 

 sists of concentric grooves and striae. 



Dimensions. — Long. 26.5 mm.; lat. 15 mm.; alt. 12 mm. 



Distinguishable from A. u/,sessa by its rounded apex, shallowness, and larger size. 

 One specimen from upj^er San Pedro series of Crawfish George's. 



Living. — Sitka to Monterey (Dall). 



Pleistocene.— San Pedro (Arnold): San Nicolas Island (Bowers). 



361. Acmaea mitra Eschscholts. 



Acmaa mitra EscH., Zool. Atlas, Vol. V, p. 18, No. i, PI. XXIII, fig. 4, 1833. Dall, Am. Jour. 

 Conch., Vol. VI, 1871, p. 241, PI. XIV, fig. i. Cooper, 7th Ann. Rept. Cal. St. Min., 

 1888, p. 228. Tryon, Man. Conch., Vol. XIII, j). 24, PI. Ill, fig. 50, 1891. Keep, 

 West Coast Shells, p. 99, fig. S5, 1892. Williamson, Proc. U. S. Nat. Mus., Vol. XV, 

 1892, p. 197. 



Scurrta mitra EsCH., Cpr., Brit. Assn. Rept., 1863, p. 650. Gabb, Pal., Cal., Vol. II, p. 87, 1869. 



