366 MAZATLAIT UNIVALVES 



Alaba, (described in English, by Messrs. Adams as a subgenni 

 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 SUPKALIRATA, n. s. 



A. t. tenui, conicd, albidd, posteafusco irregulariter strigatd ; 

 nitidd, subdiaphand ; marg'mibus spirce variantibtts ; vertice 

 nanimo, rotundato, parum declivo ; dein anfr. iv. tuberosis, 

 marginibus plus minusve parallelis, suturis parvis, tenuissimc 

 transversim lirutatis, lira spirali supramediand ; dein anfr. 

 iv. subnormalibus, l&vibus, subplanatis, conicis, suturis haud 

 impressis ; peripherld vix rotundatd, aperturd subquadratd, 

 ad basin subangulatd ; dein anfr. iii. normalibus, tumidis t 

 spiraliter tenue striatis, striis distantibus ; varicosis, varicibus 

 quoque in anf radii tribus, attingentibus, tumidis, concavis ; 

 aperturd subovali ; labro tenui, ad basin undato ; labio tenuis- 

 simo, parvo ; columelld vix intortd. 



About 50 specimens w.ere 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 Eulimella, 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 nofr 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 w r hirls become tumid, 

 their smooth surface spirally striated, the porcellanpus 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 a notch. As far as 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 



