396 Gould's Descriptions of Shells 
metricis: intus alba. Cardo valve dextre dentibus duobus instructus quorum 
antico minore, postico bifido; valvs sinistræ duobus quorum antico bifido, pos- 
tico perobliquo; dentibus lateralibus nullis; cicatricibus inconspicuis, palliali 
serie punctorum composito. 
Shell small, rather thin, subglobose, dingy white, marked with 
delicate lines of growth, which at some parts are more conspicu- 
ous than at others, and render the surface somewhat irregular ; 
beaks very nearly median, not prominent; no distinct lunule in 
front of them: ligament prominent; extremities a little above the 
middle of altitude, very nearly symmetrical. Interior white. Hinge 
with two direct teeth in the right valve, of which the anterior is 
smallest, and the posterior is bifid; and two in the left valve, of 
which the anterior is bifid and the posterior very oblique; lateral 
teeth none; muscular impressions faint, very large ; pallial impres- 
sion indistinct, composed of a series of polished dots. 
. Length four fifths of an inch; height six eighths of an inch; 
breadth half to five eighths of an inch. 
From San Diego. Lieut. Green. Santa Barbara. Col. Jewett. 
The size and globose form of this species recalls L. columbella, 
Lk., (L. Adansonii, D'Orb.): but the shell is much less solid, the 
beaks less elevated, no areas before and behind them, and the sur- 
face is not lamellar. ZL. globularis may be more like it. Some 
specimens are nearly perfect spheres, and all of them are very con- 
vex lenses. 
ARTHEMIS SACCATA (PI. XV. Fig. 2.) 
Arthemis saccata, Gould; Proc. B. S. N. H., Nov. 1851, IV. 91.) 
T. tenuis, albida, ventricosa, rotundato-rhomboidea, subequilateralis, margine 
lunula cordata, lineà impressá 
finita; valvis tumidis, postict compressis et ad marginem sinuatis; cardo alvz 
dextre dentibus binis fissis instructus, valve sinistrze dentibus tribus. 
Shell thin, white, of a rounded rhomboidal outline and ventricose 
form, the beaks being prominent, the ventral margin produced or 
pendulous and the two ends rather suddenly curved above the 
middle: surface delicately and closely striate, with a zone or !Wo 
of dusky at stages of growth; a cordate lunule is defined by an 
impressed line in front of beaks; the disk of the valves is very 
tumid, but the posteriór umbonal slope is a little constricted, mak- 
