242 MAZATLAN UNIVALVES 
continues the subsutural line; and the other, which is most 
conspicuous on younger shells, being often nearly evanescent 
in larger specimens, appears on the spire. The labrum in 
this species also resembles Adeorbis; and in one specimen is 
slightly thickened, producing a few varical ridges near the 
aperture. Another has the ultimate whirl abnormally depress- 
ed. Long. ‘025, lat. 055 by °045, div. 160°. 
Hab.—Mazatlan ; 4 perfect and 4 broken speeimens off Chama 
and Spondylus ; L’pool Col. 
Tablet 1153 contains a beautifully perfect specimen, anda 
larger one with the varical mouth. 
° 
303. VITRINELLA BIFRONTIA, 7%. S. 
V. t. subdiscoided, subdiaphand, nitente, pulcherrima, anfrac- 
tihus iv. et dimidio: carinis duabus levibus, maxime promin- 
entibus, angulatis, spiralibus, quarum una infra, una supra 
peripheriam site sunt ; carind tertia inter eas, ad peripheriam, 
parum conspicud; carind quartd posticd, haud prominente, 
prope suturam valde impressam, in spird decurrente ; ad wm- 
bilicum maximum angulata, haud carinata ; basi subplanata, 
striis duabus spiralibus, intus quadratim decussatis, extus decus~ 
satione remotiore ornata; ad spiram striis incrementt irregu- 
laribus, rugulis intus umbilicum subcrenantibus ; apertura 
quadratd, & carinis angulata, haud nisi ad carinam basalem 
anfr. penult. attingente ; spird subplanatd, anfr. ult. decumbente. 
Variat carinulis spiralibus prope suturam tintercalantibus. 
Variat quoque ad basim, stris spiralibus vix monstrantibus, 
yugulis usque ad peripheriam equaliter radiantibus. 
In the form of the base and aperture and the wrinkles of, 
growth, this species resembles Solarium : in its two prominent 
keels and scarcely united whirls it has relations with Bifrontia, 
(Omalaxis, H. & A. Ad. Gen. i. 244,) first discovered in a living 
state by the indefatigable zeal of R. M’Andrew, Esq. The 
medial keel does not project beyond the upper and lower 
ridges: the posterior keel is between the lower keel and the 
suture. The adolescent portion, which is as usual nearly 
smooth, though angulated at the spire, is almost concealed by 
the penultimate portion ; the last whirl however descends as in 
Delphinula, only touching by the anterior keel. The base is 
normally ornamented with two spiral lines, decussated in 
squares between ; with rarer decussating lines on the outer por- 
