STROBILOPS, CANADA AND UNITED STATES. 23 



fourths of a whorl (var. parietalis). The number of baso- 

 palatal folds outside of the second one (the third from, the 

 columellar), varies from three to four in adult shells, and 

 there may be either one or two of them above the periphery. 



The color of the shell varies from dark to light brown, and 

 albino shells occur (Neosho Co., Kansas) which are similar to 

 S. I. virgo in color, but have a wider umbilicus and a less 

 emerging infraparietal lamella than typical northern virgo. 



In a young shell of 1.7 mm. diameter the internal barrier 

 consists of a rudimentary columellar lamella, four long basal 

 folds and one above the periphery. In some individuals the 

 number of basal folds is increased in the late neanic stage. 

 In one young Kansas specimen, nearly ready to form the lip, 

 there are ten, including the columellar lamella (PI. 1, fig. 10) ; 

 but so large a number is very exceptional, and I have never 

 seen a fully adult shell with more than a columellar, four 

 basal and a palatal fold — six in all. The supernumerary folds 

 are evidently absorbed at the inception of the adult stage. 



Morse's figure of the spines on the parietal lamellge of 8. 

 lahyrinthica represents them as longer and stronger than in 

 any of the many shells I have opened. I conclude that his 

 figures of the internal structure are rather diagrammatic. 



la. S. lahyrinthica form virgo Pils. PI. 4, figs, 3, 4. 



Shell whitish with a faint green or yellow tint (or pale 

 brown), the lip and lamella white. Umbilicus small, con- 

 tained 10 times in the diameter. The infraparietal lamella 

 emerges somewhat more strongly than usual in lahyrinthica; 

 otherwise the lamellse and folds are the same. Height 2, diam. 

 2,5 mm. 



Maine to Minnesota and Iowa ; reported also from Arkansas ; 

 described from Sebec Lake, Piscataquis Co,, Maine, 



The albino shells are found associated with pale brown 

 specimens in the type locality, all agreeing in lamellas and 

 other characters except color. As a color-form it is recog- 

 nisable, but I believe of very little significance racially. It 

 appears to be chiefly a Canadian Zone form. 



