308 CALIFORNIA ACADEMY OF SCIENCES. 



343. Crepidula aculeata Gmelin. 



Patella aculeata Gmel., Syst. Nat., p. 3693, 1788. 



Crepidula aculeata Gmel., ^Calyptraa echinus Brod., =Calyptma hystrix Brod., ^Crepidula 

 californica NuTT. (^fide Cpr., Brit. Assn. Rept., 1856, p. 323, PI. VIII, figs. 3a, 37). 

 Cpr., Brit. Assn. Rept., 1863, p. 654. Tryon, Man. Conch., Vol. VIII, p. 129, 

 PI. XXXIX, figs. 61-65, 1886. Cooper, 7th Ann. Rept. Cal. St. Min., 1888, p. 236. 

 Dall, Bull. U. S. Nat. Mus., No. 37, 1889, p. 152. Keep, West Coast Shells, p. 76, 

 1892. Dall, Trans. Wagner Inst. Sci., Vol. Ill, Part 2, 1892, p. 357. Williamson, 

 Proc. U. S. Nat. Mus., Vol. XV, 1892, p. 203. 



Shell small, deep, thin; apex near anterior margin curved to left, smooth; surface sculptured 

 with numerous prominent rounded, discontinuous, irregular ridges from near apex to margin; margin 

 thin, crenulated; aperture subquadrate; deck oblique, thin, cupped, lower on right side than on 

 left; inner surface smooth. 



Dimensions. — Long. 11 mm.; lat. 9 mm.; alt. 6 mm. 



The specimen described was identified by Dr. Dall. The occurrence of this 

 species on both sides of the American continent is probably due to the survival of 

 an old form which has changed little since the two regions were closely connected 

 by water. 



Rare in the lower San Pedro series of San Pedro and Deadman Island. 



Living. — Monterey, south; Asia; Atlantic (Cooper). 



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



Pliocene. — San Fernando (Cooper) : De Leon Springs, Shell Creek, and 

 Alligator Creek, Florida (Dall and Willcox). 



344. Crepidula adunca Sou-erhy. 



Crepidula adunca Sby., Tank. Cat., Appen., p. 7, 1825. Cpr., Brit. Assn. Rept., 1863, p. 654. 

 Gabb, Pal. Cal., Vol. II, p. 82, 1869. Tryon, Man. Conch., Vol. VIII, p. 129, 

 PI. XXXVIII, figs. 51-55; PI. XXXVII, figs. 39, 40; PI. XXXIX, fig. 60, 1886. 

 Cooper, 7th Ann. Rept. Cal. St. Min., 1888, p. 236. Keep, West Coast Shells. 

 P- 75' fig- 60, 1892. Dall, Trans. Wagner Inst. Sci., Vol. Ill, Part 2, 1892, pp. 355, 

 358. Williamson, Proc. U. S. Nat. Mus., Vol. XV, 1892, p. 203. 



Crepidula rostriformis Gld., Proc. Bost. Soc. Nat. Hist., Vol. II, 1846, p. 160; Wilkes' Expl. 

 Exped., Vol. XII, p. 375, fig. 482, 1852. 



Crypta adunca Sby., H. & A. Adams, Gen. Rec. Moll., Vol. I, p. 369, 1853. 



Shell nearly circular at base, elevated and curved backwards to apex; apex elevated, sharp, 

 hooked, and removed from margin; surface marked with fine lamellar lines of growth; aperture 

 nearly circular; margin thin; deck short, thin in middle, thicker towards sides, with anterior edge 

 deeply curved; cavity penetrates beak from deck; deck set deep in shell. 



Dime7isio7is. — Long. 19 mm.; lat. 12.5 mm.; alt. 10.5 mm.; aperture 15 mm. x 12.5 mm. 



This shell is easily distinguishable by its elevated apex and short, curved-edged 

 deck. Dr. Dall identified the shell described. This is the West Coast form of the 

 Atlantic G. convexa Sby. 



Rather rare in the lower San Pedro series of Deadman Island and San Pedro; 

 and in the upper San Pedro series of Los Cerritos, Crawfish George's, San Pedro, and 



