1911.] NATURAL SCIENCES OF PHILADELPHIA. 189 



At Station 60 only fossil examples were taken. 

 Fig. 8. Alt, 9.8, diam. 21. 0, umbilicus 6.5 mm. (Station 62). 

 " 9. " 11.0, " 22.7, " 6.3 " ( " 61). 



(7) At Snake Gulch, below the Coconino Smelter, Station 49, the 

 shells resemble those from Station 66, having a low conoidal spire 

 and depressed last whorl which falls decidedly at the aperture. Bands 

 narrow, rather pale. 



(8) At Station 37, Snake Gulch, at the north side of the mouth of 

 Smelter Gulch, elevation 5,750 feet, the shells resemble those from 

 Station 50 (see fig. 11). 



(9) At Castle Springs, Station 79, the shells are large and dark, 

 two-banded or more or less clouded (PI. figs. 19-21, 6,750 feet elevation). 

 Similar examples are found at Riggs Spring, Station 81. 



Fig. 19. A lt, H.8, diam. 20.0 mm. (Station 79). 



"2. '• 13.5. •' 23.8 •' umbilicus 6.2 mm. (Station 79). 



" 21. " 12.C, " 23.2 " " 5.3 " ( " " ). 



Between the preceding and following stations there is an interval 



of about 13 miles over the watershed in which no Oreohelices were 



found. 



(10) Quaking Asp Canyon penetrates the Kaibab Plateau from 

 the west, where it drains into Tapeats Creek. Two-Springs Canyon 

 is a branch of the head of Quaking Asp. From the lower end of 

 Quaking Asp Canyon, Station 98, 6,500 feet elevation, to the head, 

 Station 83, 8,250 feet, there is a gradual diminution in size of the shells, 

 no doubt due to increasing aridity of the higher stations westward. 



At Station 98 the shells are very large, diam. 22 to 26 mm., but 

 typical in form and color (PL XIII, figs. 24-26). At Station 97 the 

 size averages smaller, and there are some albino shells, white with 

 translucent, greenish bands. At Stations 99, 96, 94, 93, 92, 91, 90, 

 89, 87, 88 there are similar shells, the size diminished a little (PI. XIII, 

 figs. 22, 23, Station 91, 7,000 feet). 



Stations 86, 85, 84 and 83 show shells still further diminished, adults 

 measuring, alt. 9 diam. 14 to alt. 7, diam. 11.5 mm., with 4| whorls 

 (PI. XIII, figs. 27, 28, Station 84). The color is typical; the periphery 

 angular in front and the last whorl descends only very little to the 

 aperture. These colonies show no senile features. Their develop- 

 ment has been arrested, the small number of whorls and the angular 

 periphery being characters of youth. 



At Two Springs, Station 27, the shells resemble those from Station 

 91. Farther up the canyon. Station 26, the shells became smaller,, 



