THE NAUTILUS. 135 



(5.) Patula strigosa GM. var. intersum. 



Shell umbilicated, sublenticular, depressed, thin, dark horn color, 

 more or less stained with darker chestnut. Whorls 5? or 6, some- 

 what flattened above, more convex beneath, obtusely carinated at the 

 periphery and bearing numerous coarse oblique rib-like striifi, and 

 two dark revolving bands ; suture well impressed; umbilicus large, 

 pervious ; aperture oblique, subangulated ; lip simple, thickened, 

 its terminations joined by a thick callus. 



Height of the largest specimen 5 inch, breadth f inch. 



Height of the smallest specimen tV inch, breadth fc inch. 



Habitat. Bluffs along the banks of little Salmon River, Idaho. 



Remarks. — This shell inhabits stpjie piles at the foot of a steep 

 bluff back some distance from the river. It seems to be quite rare 

 as I found but few specimens during the two or three days of my 

 stay in its vicinity, and many of them were dead. I regard it as one 

 of the most interesting shells found by me during the season, for it 

 combines the depressed angulated or keeled forms of the Haydeni 

 side of the series, Avith the sculpturing of Idahoensis, two shells 

 representing opposite characters in every respect. It thus becomes 

 the companion of Wahsatchensis, a beautiful shell combining the 

 same characters, but much more developed and connected with the 

 large elevated forms. Var. intersum fills the opposite office by 

 uniting these characters with the small depressed forms. Taken as 

 a whole, this series of shells as now completed, seems to me to offer 

 the best guide or key to the study of species that the student can 

 have. Every known external character belonging to the genus 

 Helix, is so gradually modified and blended with opposite characters, 

 that if one had the molding or making of the many and various 

 intermediate forms, he could scarcely make the series more comj^lete 

 than nature has done herself 



NOTES ON SOME NORTHERN PUPIDAE WITH DESCRIPTION OF A 

 NEW SPECIES. 



BY DR. V. STERKI. 



Vertigo tridentata Wolf. 



Has a wide distribution in the northern part of the country ; 

 originally found in Illinois, it has been collected in different parts of 



