ARNOLD — THE PALEONTOLOGY AND STRATIGRAPHY OF SAN PEDRO. 147 



Subgenus Chione Megerle. 



Shell oval, triangular or subcordiform; margins finely crenulated; hinge narrow, solid, with 

 three teeth in the right valve and two in the left, the anterior tooth longest; ligament narrow; pallial 

 sinus shallow. 



Venus gnidin Bred, is a characteristic species. 



82. Venus (Chione) fluctifraga Soiverby. 



Plate XIV, Fig. 2. 



Vemis fluctifraga Sby., Thes. Conch., 1842-1859. 



Chione fluctifraga Sbv., -\-C. callosa Sv,\.\ = Venus cortesi Slo at; = V. giddosula (Desh.) KvE. 



{fide Carpenter, Brit. Assn. Rept., 1863, pp. 641, 666). Cooper, 7th Ann. Rept. Cal. 



St. Min., 1888, p. 234. Keep, West Coast Shells, p. 187,1892. Williamson, Proc. 



U. S. Nat. Mus., Vol. XV, 1892, p. 188. 



Shell of medium size and thickness, suboval; surface roughened by radiating rows of 

 squarish blocks, this condition being caused by wide concentric ridges being cut by radiating 

 sulcations; spaces between the concentric ridges ornamented by fine, even, incremental lines; lunule 

 of same sculpture as shell, scarcely differentiated; two prominent teeth and a rudimentary anterior 

 one in the right valve; pallial sinus quite deep; muscle-impressions elongate-oval. 



Diniejisions. — Long. 25 mm.; alt. 21 mm.; diam. 15 mm. 



Distinguishable from others of this genus found in these beds by being more 

 swollen, oval rather than cordiforin in shape, thinner shelled, by the " blocked " 

 surface, and by the lunule being scarcely differentiated from the rest of the shell. 

 Specimen identified by Dr. Dall. 



Rare in upper San Pedro series of San Pedro ; one specimen, a right valve, 

 which is figured, and is now in the collection of Delos Arnold. Common in the 

 Pleistocene at Twenty-sixth Street, San Diego. 



Living. — San Pedro to San Diego; Gulf of California (Cooper). 



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

 (Arnold). 



83. Venus (Chione) gnidia Broderip £ Sowerby. 



Plate XIV, Fig. 7. 



Verms gnidia Sby., Gen. Rec. & Fos. Shells ( Venerida:), fig. 7, 1824. 



Venus gnidia Brou. & Sby., Zool. Jour., Vol. IV, 1829, p. 364; Zool. Beechey's Voyage, p. 151, PI. 



XLI, fig. 3, 1839. Reeve, Syst. Conch., Vol. I, fig. 5, 1841. Carpenter, Brit. Assn. 



Rept., 1856, p. 175; 1S63, p. 561. 

 Chione gnidia Brod. & Sby., Tryon, Syst. Conch., Vol. Ill, p. 176, PI. CXIII, fig. 14, 1884. 



Shell large, thick, subcordiform; surface ornamented by several prominent, palmate, concen- 

 tric frills and numerous squarish, radiating ribs between which are canal-like sulcations of about 

 equal width with the ribs; the ribs are sharper in outline near the beak and multiply in number both 

 by division and intercalation as the margin is approached; near the periphery, and also on the anterior 

 portion of the shell, the ridges become wider and less prominent, and in some cases almost obsolete; 

 the concentric frills become widely separated in the adult shell; lunule prominent, shows fine laminae 



