148 CALIFORNIA ACADEMY OF SCIENCES. 



of growth which arc most prominent when projections of the frills; hini;c narrow, solid; throe 

 cardinal teeth in rijjlit valve, two in left; ligament narrow; ])allial simis much shorter th.m hinule; 

 muscle- im|)rcssions distinct. 



/h'mt-'isions. — Long. 98 mm.; alt. 83 mm.; diam.62 mm.; liinulc 1 .S mm. 



This is the larjjcst of tlio i^eniis found in these (h'posits and is easily 

 cli.stin<:;iiishahh' \)\ its size, pfoiuiiient concentric frills and luiinerous radiatin<^ ribs. 

 The specimen whose dimensions are given above had twenty-fonr concentric frills 

 and about ninety radiatini;- ribs. S|)ecimcns identified by Dr. Dall. 



Rare in the upper San Pedro series of .San Pedro, whence the specimen 

 fignred came. This specimen is now in the collection of Delos Arnold. 



Living. — Gulf of California In Panama (Carpenter). 



Pleistocene. — San Pedro (Arnold). 



84. Venus (Chione) neglecta Son-erhy. 



Plate XIV, Fic. :!. 



Venus neglecla Sby., Thes. Conch., 1842-1S49. Carpenter, Brit. A.ssn. Rept., 1856, p. 306. 



Shell of medium size and thickness, suboval; surface ornamented with quite numerous, about 

 equidistant, undulating, concentric, low frills, and numerous unequal, rounded, radiating ridges^ 

 which are most prominent on the middle of the shell; lunule prominent, ornamented with minute 

 concentric and radiating sculpture; hinge and pallia! sinus are as in C. succhiia. 



Dimensions. — Long. 29.5 mm.; alt. 24 mm.; diam. 13 mm ; lunule 6 mm. 



This species is close to C succincta, but may be differentiated by its more 

 oval outline, thinner shell, relatively less diameter, and less prominent but more 

 numerous concentric frills. Specimen identified as " probably C. neglecta " by Dr. Dall. 



Rare in up[)er San Pedro series of San Pedro and TjOs Cerritos. The specimen 

 figured is from the up[>er San Pedro series at San Pedro, and is now in the collection 

 of Delos Arnold. 



Living. — -Gulf of California and Central America (Carpenter). 



Pleistocene. — San Pedro (Arnold). 



85. Venus (Chione) simillima Sovterhy. 



Venus simillima Sbv., Thes. Conch., p. 708, PI. CLIII, figs. 17, 18, 1842-1850. 

 Chione simillima Sbv., CARPE^^TER, Brit. Assn. Rept., 1863, p. 641. Cooper, 7th Ann. Rept. Cal. 

 St. Min., 1888, p. 234. Keep, West Coast Shells, p. 186, 1892. Williamson, Proc. 

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



Shell of medium size, thick, subcordiform; surface ornamented by numerous slightly 

 crenulatcd, refle.xed, concentric frills, which grow closer and closer together as the periphery is 

 approached, and by about twenty bifurcated, radiating ridges, which are largest in the middle of the 

 shell, becoming obsolete anteriorly and posteriorly, and increasing in number, but fading out as the 

 ■ periphery is approached; lunule [)rominent. ornamented with incremental laminxs hinge narrow; 

 only two prominent cardinal teeth on each valve; pallial sinus very shallow; margin crenulated. 

 Dimensions.- — Long. 40 mm. ; alt. 35 mm. ; diam. 25 mm. ; lunule 9 mm. 



