52 THE NAUTILUS. 



BIFIDABIA ABMIFEBA SAT, AND ITS TARIETIES. 



BY V. STERKI. 



It has long been known that B. armifera is variable with respect 

 to some of its features, but it seems that no attempt has been made 

 to ascertain whether there are any real, tangible varieties. Careful 

 examination of about 2,000 specimens from many places,^ during the 

 last few months, has proved that, after eliminating B. clappi as a 

 distinct species, there are several well-marked varieties, with features 

 which are of interest also in a general way. 



B. armifera (Say) typical.* Shell more or less fusiform, decid- 

 edly short to rather elongate and slender, vitreous, colorless to very 

 pale horn, or slightly milky-white; surface shining, with compara- 

 tively coarse, irregular striae; whorls 6^-8, the average being about 

 7, the last somewhat rounded, keel-like, at the base, somewhat flat- 

 tened over the palate, usually with a distinct, linear scar over the 

 lower palatal plica; aperture rather large, rounded, peristome well 

 everted, continuous, or its ends approximate, often with a connecting 

 callus; inside the palate a rather strong, white callus into which the 

 palatal plicae merge; parieto-angular lamellae rather large and long, 

 distinctly complex, the angular connecting with the peristome, the 

 spur * of the parietal small but distinct; columellar massive, encircling 

 the column, with an annex downward and inward ; inferior col- 

 umellar variable as to size, shape and position, sometimes a mere 

 callus, often wanting; lower palatal plica regular, rather long, stout, 

 upper palatal much shorter and smaller; suprapalatal distinct or slight 

 or wanting; an interpalatal is not infrequent. 



Alt. 3.5-5, average 4-4.5, diam, 2.2-2.5 mm. 



Distributed over the whole area covered by the species. 



B. a. interpres, n. var. Near the typical form, generally some- 

 what slender; inferior columellar lam. rather high up, the base is 

 narrow inside and more keel-like outside; the aperture is narrowly 

 rounded at the base, and from this feature specimens are easily rec- 

 ognized. More than any other form this shows clearly that the 

 so-called " basal " is really an inferior columellar, 



1 There are 160 entries in my collection of B. armifera and varieties, and 

 many others were received for examination. 



* Dr. Pilsbry had the kindness to look up Say's original specimens in the 

 collection of the Phila. Acad., and wrote me that they are of this form. 



'See The Nautilus, XXII, p. 108, foot-note. 



