62 PROCEEDINGS OF THE ACADEMY OF [Feb., 



Diam. in mm 23 23 23 23 22.8 



Alt. in mm 14 13.5 13.1 13 13.5 



The total variation in diameter in this colony is 3.2 mm. The 

 variation in altitude is comparatively greater, owing to the varying 

 degree of elevation of the spire. 70 per cent, of the lot are from 24 to 

 25 mm. in diameter. Figures 6-9 were drawn from specimens of the 

 type lot from this Station. 



Station 4. Cleft in the rocky summit of hill at fork of Big Emigrant 

 Canyon, facing mouth of canyon (pi. I, fig. 10). Ten specimens, two 

 alive, measure: 



Diam. in mm 26 25.5 25.5 25 25 25 24 23.7 23.3 23.3 



Alt, in mm 15 16 14.7 16 15 15 14.7 13.3 13 13 



They differ from the type lot in having the aperture barely per- 

 ceptibly larger, umbilicus smaller. In a specimen of the type lot 

 25 mm. in diam. the aperture measures 11.4x13.1 mm. In one of 

 the same diameter from Station 4 it is 12 x 13.4 mm. 



Spirally striate forms. — The shells from Stations 2, 3, 5, 6 — Big 

 Emigrant Mountain and Cross J Mountain — usually show numerous 

 spiral stria 1 on the upper surface of the last whorl, but this character 

 is variable; in some shells of each lot no spiral stria can be made out, 



Station 2. Close to the creek in the middle branch of Big Emigrant 

 Canyon, under stones. Three dead shells measuring 23.5, 22.3 and 

 21.8 mm., and similar to those from Big Emigrant Mountain. This 

 place is probably about 1,000 feet lower than the type locality. 



Station 3. Big Emigrant Mountain. This name is given to a 

 mountain about four miles above the fork of Big Emigrant Canyon 

 on the left side of the east branch. November 11 and 12 it was visited. 

 On the side toward the canyon, under a rocky bluff, under stones 

 among scrub oaks (Queixus hypoleucal) , in a situation resembling that 

 of Sonorella bowiensis, numerous specimens of a small form were 

 taken, almost all dead shells. Sixty-five adults taken measure in 

 diameter as follows : 



Diam. in mm 20.5 20 19.5 19.3 19 18.8 18.5 18.3 



No. of shells 11 4 1 6 4 7 6 



Diam. in mm 18 17.8 17.5 17.3 17 16.5 16 15.5 



No. of shells 7 4 4 5 7 3 4 1 



The shells are in the average more depressed than typical »S. optata. 

 The largest measures, alt. 10.5, diam. 20.5, aperture 9.2 x 11.2 mm. 

 Another, alt. 10.5, diam. 18.5, aperture 8.3 x 9.9 mm. There are 



