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, lot. '055 by '045, div. 160. 



Slab. Mazatlan ; 4 perfect and 4 broken specimens off Chania 

 and Spondylus ; L'pool Col. 



Tablet 1153 contains a beautifully perfect specimen, and a 

 larger one with the varical mouth. 



303. VlTRINELLA BIFKONTIA, n. S. ' 



V. t. subdiscoided, subdiapkand, nitente, pulcJierrimd, anfrac- 

 tibus iv. et dimidio : carinis duabus Icevibus, maxime promin- 

 entibus, angulatis, spiralibus, quarum una infra, una supra 

 peripJieriam sitce sunt ; carind tertid inter eas, ad peripkeriam, 

 parum conspicud ; carind quartd poslicd, hand prominente, 

 props suturam valde impressam, in spird decurrente ; ad urn- 

 bilicum maximum angulatd, hand carinatd ; basi subplanatd, 

 striis duabus spiralibus, intus quadratim decussatis, extus decus- 

 satione remotiore ornatd ; ad spiram striis incrementi irregu- 

 laribus, rugulis intus umbilicum subcrenantibus ; aperturd 

 guadratd, a carinis angulatd, hand nisi ad carinam basalem 

 anfr. penult, attingente ; spird subplanatd, anfr. ult. decumbent e. 



Variat carinulis spiralibus prope suturam inter calantib us* 



Variat quoqiw ad basim, striis spiralibus vix monstrantibus, 

 rugulis usque ad peripJieriam cequaliter 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, S. fy 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- 



