ARNOLD — THE PALEONTOLOCxY AND STRATIGRAPHY OF SAN PEDRO. 169 



Distinguishable from Mncoma by the prominent ligaraental projection, hinge, 

 and less angular asj)ect. Sj^ecimens identified by Dr. Dall. 



Rather rare in the upper San Pedro series at San Pedro and Los Cerritos. 



• Living. — Santa Barbara to San Diego (Carpenter). 



Pleistocene. — San Pedro (Arnold). 



Genus Tagelus Gray. 



Beaks median or subposterior; teeth two in each valve, simple, pedunculate; valves without 

 constriction or clavicle, straight; pallial sinus deep, reaching to or beyond the beaks; posterior 

 adductor scar rounded; pallial sinus with the ventral part partially coalescent with the pallial line. 



Type, Solen gihhus Spengler. 



117. Tagelus calif ornianus Conrad. 



Soleciirliis calif orniajnis don., ]o\n. Phil. Acad. Sci., Vol. VII, 1837, p. 233, PI. XVIII, fig. 3. 



Carpenter, Brit. Assn. Rept., 1863, p. 638. Cooper, 7th Ann. Rcpt. Cal. St. 



Min., 1888, p. 265. Keep, West Coast Shells, p. 201, fig. 172, 1892. 

 Tagelus calif ornianus Coi^., Dall, Proc. U. S. Nat. Mus., Vol. XV, 1892, p. 184. Dall, Trans. 



Wagner Inst. Sci., Vol. Ill, Part 5, 1900, p. 984. 



Shell of medium size, oblong-oval, convex, thin; umbones about central; posterior dorsal 

 margin runs straight back from umbo parallel with base; anterior dorsal margin slightly depressed, 

 beginning a little below and in front of umbo, parallel with base; extremities evenly rounded; basal 

 margin slightly contracted in middle; ligamental area slightly projecting; cardinal teeth, two in each 

 valve, sharp and thin; pallial sinus long and wide, pointed. 



Dimensio7is. — Long. 80 mm.; alt. 22 mm.; diam. 13 mm. 



Specimens identified by Dr. Dall. 



Rare in the lower San Pedro series at Deadman Island and San Pedro; com- 

 mon in the upper San Pedro series at Deadman Island, Los Cerritos, Crawfish 

 George's, San Pedro, and Long Beach. Also found in the Pleistocene at Twenty- 

 sixth Street, San Diego. 



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



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

 San Diego (Arnold). 



Pliocene.^San Diego (Dall). 



Family XXXIIl. DONACID^. 



Genus Donax (Linne) Lamarck. 



Shell elongate, smooth, with no posterior carination; ventral margins with obsolete serra- 

 tion; cardinal teeth two in each valve, the larger often bifid; laterals both in the left valve, the 

 anterior hardly distinguishable from the margin, of which it is a sort of modification. 



Donax trunculus Linne is a characteristic species. 



(22) January 10, laoa. 



