STROBILOPS, CANADA AND UNITED STATES. 27 



which the lamella is a little short of one whorl long, as will be 

 seen on comparing pi. 2, figs. 3 (floridana) and 5 (texasiana). 

 However, on examining long series I fiiid some examples of 

 floridana in which the parietal lamella is not over three- 

 fourths of a whorl long, so that the distinction between 

 floridana and texasiana is not a complete one, though obvious 

 in most examples. There are also shells which approach the 

 long-lamellate parietalis form of la'hyrinthica rather closely, 

 though the coarser ribbing of the base in floridana is generally 

 a differential character. 



It is sometimes quite elevated, as in the second measure- 

 ment above, but the high examples occur in lots "with lower 

 specimens. 



3. Strobilops affinis Pilsbry. PI. 3, figs. 1-5. 



The shell is convexly conic with obtusely angular peri- 

 phery; the base moderately convex, becoming rather strongly 

 so in its last third ; glossy, brown, with pale apex ; narrowly 

 umbilicate, the umbilicus contained about 1^2 to 8 times in 

 the diameter. There are 6 moderately convex wiiorls, in- 

 creasing very slowly, the first two smooth, the rest sculptured 

 with narrow, somewhat retractive ribs. The first half of the 

 base is smooth, the ribs barely passing over the peripheral 

 angle and reappearing within the umbilicus, but they continue 

 weakly over the last half. The aperture is semilunar, oblique. 

 Peristome is well expanded, thickened within, its face convex 

 and fleshy-bro^\^l in color. Parietal callus moderately strong. 

 The parietal lamella emerges to the edge of the callus and 

 penetrates inward about two-thirds of a whorl. The infra- 

 parietal lamella is low and weak, deeply immersed, not visible 

 in a front or basal view. Interparietal lamella short and very- 

 weak. A third of a whorl within there is an obliquely radial 

 series of about 8 folds : a short low lamella on the columellar 

 axis, follow^ed by two folds larger and higher than the rest, 

 and an oblique series running to the suture, composed of 4 to 

 7 short subequal folds (fig. 4). 



Height 2.5, diam. 2.75 mm. 



Massachusetts to Minnesota and Kansas, south to northern 



