156 CALIFORNIA ACADEMY OF SCIENCES. 



Distinguishable from P. carditoides by its smaller size, narrower form, thinner 

 shell, and coarser sculpture. Specimens of this same species in the State Museum 

 collection at the University of California, Berkeley, are labeled P. cognata Adams. 

 Specimens identified by Dr. Dall. 



Rare in the lower San Pedro series at Deadman Island, and the upper San 

 Pedro series at Los Cerritos and San Pedro. 



Living. — Mazatlan to Peru (Carpenter). 



Pleistocene. — San Pedro (Arnold; Blake.) 



Pliocene (?). — Los Angeles City (Williamson). 



97. Petricola (Petricolaria) cognata C. B. Adams. 



Pelrkola cognala C. B. Ads., Cat. Panama Shells; Ann. N. Y. Lye. Nat. Hist., Vol. V, 1852, 

 p. 510. Cpr., Brit. Assn. Rept., 1856, p. 363; Proc. Zool. Soc, 1863, p. 367. 



Shell of medium size, much elongated, transverse, conve.x, thin, equivalve; beaks small, near 

 anterior e.xtremity, turned forward, slightly elevated; anterior extremity short, evenly, pointedly 

 rounded; posterior extremity long, evenly, pointedly rounded; surface of shell, anterior to a line 

 running obliquely backwards from the beaks, sculptured by ten or eleven prominent, narrow, 

 squamosely spined, radiating ridges; surface posterior to this line ornamented by finer radiating lines; 

 rather prominent incremental lines over the whole surface; hinge of left valve consists of a curved, 

 saddle-shaped process of two teeth, one of which is bifid; hinge of right valve smaller and straighter 

 with less prominent division of teeth. 



Dimensions. — Long. 36 mm.; alt. 10.5 mm.; diam. 10 mm.; beaks to anterior extremity 

 6 mm.; to posterior extremity 30 mm. 



The line of demarkation between the fine and prominent radiating sculpture 

 in this species is not marked as in the Plioladidre. Distinguishable from P. denticnlafa 

 by more prominent sculpture anteriorly, longer shell, more prominent hinge-teeth and 

 more anterior beaks. P. cognata is close to the Atlantic P, plioladiformis. Some 

 authorities, notably Carpenter, unite the two forms. 



Rare in the upper San Pedro series at the lumber yard at San Pedro and 

 at Deadman Island. 



Living. — San Pedro to Panama (Dall, m.ss.). 



Pleistocene. — San Pedro (Arnold). 



Superfamily TELLINACEA. 



Family XXX. TELLINID^. 



Genus Tellina Linne. 



Subgenus Mcerella Fiiichei-. 



Shell small, compressed, hardly folded, acute behind, rounded in front, with feeble, concentric 

 sculpture; left laterals obsolete; no interior radii; the sinus long, coalescent with the pailial 

 line below. ^ 



Type, Pellina donncina (Linnr). 



