366 MAZATLAN UNIVALVES 
Alaba, (described in English by Messrs. Adams as a subgenus 
of Cerithiopsis,) there did not appear cause for adding another 
name for those species which do not accord with their diagnosis. 
The description of Tuberia is however retained, in order to 
include the whole group. Their true position, of course, can 
only be satisfactorily shewn when the animals have been 
examined. 
425. ALABA SUPRALIRATA, 2. S. 
A. t. tenui, conicd, albidd, postea fusco irregulariter strigaté ; 
nitidd, subdiaphand ; marginibus spire variantibus ; vertice 
minimo, rotundato, parum declivo; dein anfr. iv. tuberosis, 
marginibus plus minusve parallelis, suturis parvis, tenuissime 
transversim lirulatis, lird spirali supramediana ; dein anfr. 
iv. subnormalibus, levibus, subplanatis, conicis, suturis haud 
impressis ; peripheria vie rotundatd, apertura subquadratd, 
ad basin subangulata ; dein anfr. ii. normalibus, tumidis, 
spiraliter tenue striatis, striis distantibus ; varicosis, varicibus 
quoque in anfractu tribus, attingentibus, tumidis, concavis ; 
apertura subovali ; labro tenui, ad basin undato ; labio tenuis- 
simo, parvo ; columella vix intortd. 
About 50 specimens were found of this remarkable shell ; 
but most of them so very imperfect, and so different in char- 
acter at different periods of growth, that only the late and 
fortunate discovery of a fresh adult specimen, led to their 
identification. In its usual adolescent state, it might rank as 
a EKulimella, but for the want of the Chemnitzoid apex. It 
has one whirl, sufficiently sloping to give the top of the striated 
portion a mammillated appearance. The first four whirls look 
like a thimble, and differ from the rest not only in sculpture, 
but in the margins which are nearly parallel ; while afterwards 
they are more or less divergent, resembling in their irregularity 
some species of Stylifer. After however making four whirls 
in an apparently normal condition, it changes again, and as- 
sumes a Bittioid aspect. The flattened whirls become tumid, 
their smooth surface spirally striated, the porcellanous white a 
rusty brown in irregular stripes, and the periphery rendered 
irregular by tumid hollow varices, three in a whirl. The 
mouth which has always been angular at the base of the 
columella, now develops a very slight wave, scarcely amounting 
to anotch. As faras the specimens shew, this is the end of its 
changes. It most closely resembles a W. Indian species, 
Cingula tervaricosa, C. B. Ad., which however is larger, with 
