ARNOLD— THE PALEONTOLOGY AND STKATIGEAPHY OF SAN PEDRO. 161 



Subgenus Macoma s. s. 



Shell subtrigonal, the periostracum conspicuous; usually colorless, or, if colored, without 

 color pattern; flexure well marked; the pallial sinus coalescent with the pallial line below, and often 

 discrepant in the two valves; inhabiting the cooler seas, and especially boreal waters. 



104. Macoma calcarea Gmelin. 



Plate XVI, Fig. 2. 



Tellina calcarea, teste ovala, etc., Chem., Conch. Cab., Vol. VI, p. 140, Pi. XIII, fig. 136, 1782. 



Tellina calcarea, Gmelin, Syst. Nat., Ed. VI, p. 3236, No. 38, 1792. 



Macoma calcarea Chem. = Sanguiiiolaria californica Con. = Tellina pedroana Con. = Tellina 



ienera Leach {fide Gabb, Pal. Cal., Vol. II, p. 124, 1869). Cooper, 7th Ann. Rept. 



Gal. St. Min., 1888, p. 248. 

 Macoma calcarea GwEiAii. =^ Tellina lata Gmelin. = Tellina sudulosa Spenglkr. = Macoma tenera 



Leach = Tellina proxima (Brown) Sby. = Telli>ia sordida Covrnovy . = Sanguino- 



laria sordida Gld. {fide Dall, Trans. Wagner Inst. Sci., Vol. Ill, Part 5, 1900). 



Shell of medium size, suboval, slightly convex, inequilateral, thin; anterior end shorter than 

 posterior, with fold running from apex to lower anterior extremity, which is biangular; anterior dorsal 

 margin straight; anterior end evenly rounded; beaks anterior to middle, small, inconspicuous; 

 surface sculptured by fine incremental lines; two cardinal teeth on left valve, anterior one bifid; pallial 

 sinus large. 



Dimcnsio7is. — Long. 18.2 mm.; beak to anterior extremity 8.2 mm.; to posterior extremity 

 10 mm.; alt. 13.5 mm.; diam. 5.2 mm. 



This species is distinguishable from M. yoldiformis by its more prominent fold 

 and much broader form; distinguished from others of this genus found in these 

 deposits by having the anterior (folded and angular) end shorter than the posterior 

 end. Specimens identified by Dr. Dall. Specimens of this species are labeled "J/. 

 expansa " in the State Museum Collection, at the University of California, at Berkeley. 



Several specimens from the lower San Pedro series and Pliocene of Deadman 

 Island. Tiie specimen figured is from the lower San Pedro series at Deadman 

 Island, and is now in the collection of Delos Arnold. 



Living. — Arctic and boreal seas, south on Atlantic Coast to Long Island 

 Sound, on Pacific Coast to Oregon and Northern Japan (Dall). 



Pleistocene. — Scandinavia; Scotland; Greenland; Siberia; Alaska (Dall) : San 

 Pedro (Arnold). 



Pliocene. — San Pedro (Arnold). 



105. Macoma indentata Carpenter. 



Plate XVI, Fig. 1. 



Macoma indentata Cpr., Brit. Assn. Rept., 1863, p. 639. Cooper, 7th Ann. Rept. Cal. St. Min., 1888, 

 p. 248. Keep, West Coast Shells, p. 195, 1892. Williamson, Proc. U. S. Nat. Mus., 

 Vol. XV, 1892, p. 185. Dall, Trans. Wagner Inst. Sci., Vol. Ill, Part 5, 1900, p. 1052. 



Shell of medium size, rather narrow, suboval, compressed, thin; umbones slightly posterior 

 to center; anterior end long and evenly rounded; posterior dorsal line straight; ventral line near 



( 21 ) January 9, 1903, 



