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. 



