AKNOLD-THE PALEONTOLOGY AND STBATIGBAPHT OF SAN PEDRO. 163 



107. Macoma nasuta Conrad. 



Plate XVI, Fig. 3. 



Tellina nasuta CoN., Jour. Phil. Acad. Sci., Vol. VII, 1837, p. 258. 



Mcuoma Tiasula Con. = M. tersa Gld., (yff/i' Carpenter, Brit. Assn. Rept., 1863, p. 639). Gabb, 



Pal. Cal., Vol. II, p. 93, i86q. Cooper, 7th Ann. Rept. Cal. St. Min., 1888, p. 248. 



Keep, West Coast Shells, p. 194, fig. 165, 1892. Williamson, Proc. U. S. Nat. 



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



P- 1053- 

 Shell of medium size, ovate, compressed, thin; anterior side dilated; posterior side cunei- 

 form, extremity truncated much above the line of the base; posterior dorsal margin straight to angle 

 where it joins line of truncation ; fold carinated on the right valve ; umbones slightly anterior to 

 center, slightly prominent; two prominent narrow cardinal teeth in each valve; no laterals; ligament 

 external, long, straight, narrow; pallial sinus large, expanding interiorly, that of the left valve joining 

 anterior muscle-impression at its lower posterior angle. 



Dimensions. — Long. 76 mm.; alt. 54 mm.; diam. 23 mm.; umbo to anterior end 31 mm.: 

 to posterior end 45 mm. 



Distinguishable from J/, secta b}' smaller size, less convex valves, less alti- 

 tude, longer, straight posterior margin, and longer, less prominent ligamental callus; 

 from M. inquinata by larger, longer shell, less convex valves, less relative altitude, 

 straight dorsal margin witli truncation posteriorly, and by less central umbones; from 

 M. yoldiformls by more cuneiform posterior extremity, long, straight posterior dorsal 

 margin, and by having the beaks anterior to center rather than posterior; from 

 M. identata by beaks being more anterior, being broader, and by lacking the promi- 

 nent folds, indentation of ventral margin, and prominent projection of posterior 

 extremity; from M. kelseyi, which closel}- resembles it, by broader shell, and more 

 oblique truncation of posterior extremity. Specimens identified by Dr. Dall. 



Rather common in the lower San Pedro series at Deadman Island and San 

 Pedro, and the upper San Pedro series at Los Cerritos, Long Beach, Crawfish 

 George's, Deadman Island, and San Pedro. The upper San Pedro strata afiford 

 larger specimens, as a rule, than those found in the lower San Pedro. 



Found also in the Pliocene at Pacific Beach, and in the Pleistocene at Spanish 

 Bight and Pacific Beach, San Diego, and in the Pleistocene at Barlow's ranch, and 

 the old ditch, Ventura. 



The specimen figured is from the upper San Pedro series at San Pedro, and 

 is now in the collection of Delos Arnold. 



Living. — Alaska to San Diego; Kamtschatka (Cooper). 



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

 Ventura (Arnold). 



Pliocene. — Eagle Prairie and Danger Creek, Humboldt County; Santa Rosa; 

 San Fernando (Cooper): San Diego (Arnold). 



Pliocene. — Sunol, Alameda County; Foxin's, Santa Barbara County (Cooper). 



