126 THE NAUTILUS. 



and short ovoid (f. curta)." (Sterki, Land and Fresh-water Mol- 

 lusca in the Vicinity of New Philadelphia, etc., p. 5, 1894.) 



BIFIDAKIA TAPPANIANA (C. B. Adams). Figs. 42 to 53. 



The shell is larger than pentodon, markedly conic though obtuse ; 

 only one tooth on the parietal wall, usually 6 on the columellar, 

 basal and outer margins, those on the latter standing on a strong rib. 

 Lower palatal tooth usually not so long and entering as in B. pentodon. 



Distribution, Ontario to the Gulf of Mexico, west to Iowa and 

 Kansas, southwest to Arizona, but not known from the southeastern 

 Atlantic States, Virginia to Florida. 



This is the form now everywhere known as "pentodon Say." It 

 is often a difficult question, upon which no two experts might agree, 

 whether to refer a certain specimen to tappaniana or to some form of 

 pentodon, since while the larger size and globose-conic shape are 

 characteristic of tappaniana, yet intermediate sizes and shapes occur 

 occasionally, so that we disclaim any intention of setting up a defi- 

 nite boundary between the forms. It can only be claimed that the 

 great majority of lots are quite readily separable. The variations in 

 size and shape are well shown in the figures. Figs. 42, 43, Phila- 

 delphia; 44, Buckfield, Me. ; 45, Ithaca, N. Y. ; 46-48, Duchess Co., 

 N. Y. ; 49-52, Washington, D. C. ; 53, Oak Creek, Arizona. The 

 original description follows : 



" Pupa tappaniana Ward, inedit. Shell very small, pale horn- 

 color, translucent, tapering above the penultimate whorl ; whorls a 

 little more than five, convex, with a well-impressed suture ; aperture 

 sub-orbicular (the penult, whorl cutting oflf about one-third of the 

 circle), about one-third of the length of the shell ; margin sharp, with 

 a narrow contraction in the submargin, beneath which is a thicken- 

 ing within, on which are the labial teeth ; teeth eight, five primary 

 and three secondary ; of the former the largest is on the penultimate 

 whorl, the next largest on the left side of the aperture ; at the base, 

 beginning at the left hand, is a primary, then a secondary, a primary, 

 a secondary, a primary and another secondary, extending nearly to 

 the upper extremity of the right margin ; the last three primaries are 

 not constant in size ; umbilicus open. Length 0.08 inch ; breadth 

 0.05 inch. 



" This species is easily distinguished from the preceding (P. con- 

 tracta) by its teeth." ((?. B. Adams, History of Vermont, Z. 

 Thompson, 1842, p. 158.) 



