318 CALIFORNIA ACADEMY OF SCIENCES. 



359. Acmaea insessa Hinds. 



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



Nacella incessa Hds., Cpr., Brit. Assn. Rept., 1863, p. 650. Gabb, Pal. Cal., Vol. H, p. 87, 1869. 



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



fig. 91, 1892. 

 Acmaa insessa Hds., Dall, Am. Jour. Conch., Vol. VI, 1S71, p. 244, PI. XIV, fig. 3. Tryon, 



Man. Conch., Vol. XIII, p. 18, PI. VI, figs. 36, 37, 1891. 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 strise; margin inclined to be compressed as the shell grows old; ape.x slightly anterior. 



Dimensions. — Long. 17 mm.; lat. 10 mm.; alt. 11 mm. 



Found in the Pliocene of Deadman Island; the lower San Pedro series of 

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

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

 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. AcmEea instabilis Gould. 



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



Nacella i?is/adilis Gld., Cpr., Brit. Assn. Rept., 1863, p. 650. Keep, West Coast Shells, p. 103, 



1892. 

 Acmesa instabilis Gld., Dall, Am. Jour. Conch., Vol. VI, 1871, p. 245. Tryon, Man. Conch., 



Vol. XIII, p. 18, PI. VI, figs. 32, 2,:>^ 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 strite. 



Bimensio9is. — Long. 26.5 mm.; lat. 15 mm.; alt. 12 mm. 



Distinguishable from A. iiisessa by its rounded apex, shallowness, and larger size. 

 One specimen from upper San Pedro series of Crawfish George's. 



Living. — Sitka to Monterey (Dall). 



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



361. Acmaea mitra Eschscholtz. 



Acmtsa 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, p. 24, PI. Ill, fig. 50, 1891. Keep, 

 West Coast Shells, p. 99, fig. 85, 1892. Williamson, Proc. U. S. Nat. Mus., Vol. XV, 

 1892, p. 197. 



Scurriamilra EscH., Cpr., Brit. Assn. Rept., 1863, p. 650. Gabb, Pal.^Cal., Vol. II, p. 87, 1869. 



