ARNOLD — THE PALEONTOLOGY AND STRATIGRAPHY OF SAN PEDRO. 143 



77. Tivela crassatelloides Conrad. 



Cytherea {Trigonella) crassatelloides Con., Jour. Phil. Acad. Sci. , Vol. VII, 1837, p. 253, PI. XIX, 



fig. 17. Hinds, Voyage Sulpher, p. 65, PI. XXI, fig. i, 1844. 

 Donax slidtorum Marve, Linn., Lyst. Conch., pp. 37, 40, PI. IX, fig. 7, 1823. Gray, Index. Test. 



Suppl., PI. II i^Donax), fig. 2, 1828. 

 Cytherea crassatelloides Con., Hanley, Descr. Cat. Rec. Bivalve Shells, p. 106, 1843. Sowerbv, 



Thes. Conch., Vol. II, p. 612, PI. CXXVII, figs. 1-3. Reeve, Icon. Conch., Vol. XIV, 



PI. I, fig. 3, 1864. 

 Cytherea slidtorum Gray, Hanley, Descriptive Cat. Rec. Bivalve Shells, p. 106, 1843. 

 Trigonella crassatelloides Con., Jour. Phil. Acad. Sci., Vol. I, 1849, p. 213. 

 Trigo/iia crassatelloides CoK., Deshayes, Cat. Conch. Coll. B. M., Part i, p. 46, 1S53. 

 Trigonia stultorum Gray, Deshayes, Cat. Conch. Coll. B. M., Part i, p. 46, 1853. 

 Pachydesma crassatelloides CoN., Proc. Phil. Acad. Sci., 1854, p. 121. Carpenter, Brit. Assn- 



Rept. 1863, p. 640; =Cytherea solidissima Phil., Gabb, Pal. Cal. Vol. II, p. 96, i86g. 



Cooper, 7th. Ann. Rept. Cal. St. Min., 18S8, p. 256. Keep, West Coast Shells, p. 



189, fig. 162, 1892. 

 Tivela crassatelloides CoN., Williamson, Proc. U. S. Nat. Mus., Vol. XV, 1892, p. 187. 

 Cytherea {Tivela) crassatelloides Con., Stearns, Proc. U. S. Nat. Mus., Vol. XXI, 1898, pp. 371- 



378, PI. XXIII-XXV. Stearns, Nautilus, Vol. XIII, 1899, p. 73. 



Shell large, subequilateral, trigonal, depressed, thick; umbones subcentral, small; anterior 

 extremity shorter and more obtusely rounded than posterior; anterior dorsal margin nearly straight 

 slopes down obliquely from umbo ; posterior dorsal margin slightly concave in fi-ont of umbo, 

 slope less than anterior; posterior extremity narrower than anterior; three prominent, thick, cardinal 

 teeth in each valve, anterior lateral tooth elongated; pallial sinus short, angular. 



Dimensions. — Long. 80 mm.; alt. 55 mm.; diam. 30 mm. 



The Pleistocene specimens have a tendency toward more central umbones 

 than do the living forms. This species is distinguishable from the Mactras by its 

 very thick shell and heavy cardinal teeth. Specimens identified by Dr. Dall. 



Common in the upper San Pedro series of San Pedro, Los Cerritos, Long- 

 Beach, Crawfi.sh George's and Deadman Island; rare in the lower San Pedro series 

 of Deadman Island. Found also in the Pleistocene of Twenty-sixth Street and Spanish 

 Bight, San Diego. 



Living. — Santa Cruz to San Diego (Cooper). 



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

 (Arnold). 



Genus Callista Poli. 



Shell oval, transverse, inequilateral; pallial sinus suboval, profound. 



Cytherea erycina Linn, is a characteristic species. 



78. Callista newcombiana Gahb. 



Lioconcha ne^vcombiana Gabb, Proc. Cal. Acad. Sci., 1865, p. 189; Pal. Cal., Vol. II, p. 96, i86g. 

 Callista newcombiana Gabb, Cooper, 7th Ann. Rept. Cal. St. Min., 1888, p. 231. Williamson, 

 Proc. U. S. Nat. Mus., Vol. XV, 1892, p. 187, PI. XXIII, fig. 4. 



Shell thin, trigonally ventricose, polished, marked by minute concentric strize; beaks large, 

 subcentral; anterior end prominent, narrowly rounded; posterior end a little the widest; base arcuate; 



