1911.] NATURAL SCIENCES OF PHILADELPHIA, 179 
retractor muscle inserts on the epiphallus. The vagina is rather short 
and slender. Atrium longer than usual in Sonorella. Length of the 
penis, 4.5 mm.; penis-papilla, 2 mm.; vagina, 3 mm.; spermatheca 
and duct, 21.5 mm. 
Fig. 3.—Genitalia of Sonorella coloradoensis. A, Spectacle Cove. B, bandless 
form from White Creek, Station G. 
A specimen of the bandless form from White Creek, a branch of 
Shinumo Creek, shows only slight differences in the genitalia from the 
“Spectacle Cove” form. The atrium is shorter; penis-papilla more 
cylindric and blunter. Length of penis, 5 mm.; epiphallus, 4.7 mm. ; 
penis-papilla, 2 mm.; vagina, 3.8 mm. 
While S. coloradoensis seems to be generally distributed in the 
Grand Canyon, the colonies, except near the rim, are isolated and 
mostly small. Except during wet weather, the snails adhere to 
eruptive or metamorphic rocks, making white circles thereon like 
other Sonorellas. Specimens were taken by us at the following places: 
(South side of the Colorado River.) 
(1) Bass’s Station, on the Grand Canyon R. R., about four miles 
south of the Grand Canyon. The shells vary from alt. 10.5, diam. 16 
mm., to alt. 9.8, diam. 15 mm. 
(2) Upper talus along the Bright Angel Trail from 100 to 400 feet 
below the rim. The specimens are like those from Spectacle Cove, 
noticed below. 
