158 PUPILLA, AMERICAN. 



P. muscorum has a far greater zonal or climatic range, as 

 well as a wider geographic distribution in the Palaearctic Re- 

 gion than in America. Our form was doubtless derived from 

 the northern herd of Siberia and northern Europe by way of 

 Alaska, probably in interglacial or Pleistocene time, and has 

 not yet become adapted to warm climates such as the circum- 

 Mediterranean zone which it inhabits in the Old World. 



Three-tooth mutations occur as in Europe : the typical 

 form, in which there are no teeth (pi. 18, fig. 15, Mt. Desert, 

 Maine). 



Mut. marginata Drap. (unidentata C. Pfr.). A small, short 

 parietal lamella developed (pi. 18, figs. 13, 14). This includes 

 P. badia C. B. Ad. 



Mut. masclaryana Palad. (~bigranata auct.). A tubercular 

 or short parietal lamella and a small, tubercular lower-palatal 

 fold present (pi. 18, fig. 12). 



Mutation having a columellar tooth more or less well de- 

 veloped, pi. 19, fig. 14. White Oaks, New Mexico. This form 

 has been noticed in America only in the mountain states of 

 the West. Boettger has mentioned its occurrence in France. 



The typical mutation, without teeth, is the most abundant 

 and widely-spread in America. Specimens of it usually occur 

 in lots containing marginata and masclaryana, such colonies 

 being evidently hybrid. 



A large series from High Pines, Duxbury, Mass., consists 

 of very thin, toothless shells, with the crest low or very low, 

 not paler, the lip scarcely calloused within. They run down 

 to 3 mm. long, with 5% whorls, and resemble the western P. 

 hebes. Similar shells occur as far south as Atlantic City, 

 N. J., in copses in the salt marshes. 



Most of the Rocky Mountain specimens seen are of the 

 typical toothless form, and none have a palatal tooth. They 

 vary widely in size. Two from Holbrook, Arizona, measure: 



Length 3.85, diam. 1.9 mm., 6% whorls. 



Length 2.75, diam. 1.5 mm., 5% whorls. 



Pupitta mwcorum form xerobw Pils., pi. 19, fig. 11, de- 

 scribed from an arid sandstone butte near Duran, New Mex- 

 ico, at 6700-6800 ft., is a small, compact form which I took to 



