382 PROCEEDINGS OF THE ACADEMY OF [June, 



At the adjacent Station 8, eastward and slightly higher, the 

 shells average smaller — about 10.5 mm. long — but are otherwise 

 similar. 



Station 29. Bear Gulch, near top, and Station 30, ridge west of 

 Bear Gulch, typical shells. 



Stations 31, 32, on the east side, and Station 33 on the west side 

 of Soren Gulch, typical shells. 



Station 34- A small limestone hill in Middlemarch Canyon. 

 The shells have perceptibly coarser sculptures than in the types, 

 about 70 riblets on the penultimate whorl. One internal lamella, 

 the axial. 



Station 35. Cochise Peak. Similar to the shells from Station 34. 



Station 36. Small limestone hills eastward on the mesa of Middle- 

 march Canyon. The shells here are smaller than typical millestriata, 

 and vary from the typical fine ribbing to somewhat coarser (PL XV, 

 figs. 4, 4a, the prevalent form), and a few are as coarsely sculptured 

 as H. campestris cochisei, the coarsest having 48 ribs on the penulti- 

 mate whorl. The proportions of diameter to length also vary a 

 good deal, as shown in the figures and measurements. All the speci- 

 mens opened have a single lamella, the axial. 



Length 9.5, diam. 3.6 mm.; whorls 11. 



9.1, " 3.3 " " lOf. 

 9.6, " 3.1 " " 11. 



9.2, " 3.5 " " 10^. 

 8, " 3.2 " " 10. 



Station 37. Another colony near the preceding, consists of very 

 small shells. (PI. XV, figs. 5 to 5c.) 



Length 9, diam. 3.2 mm.; whorls 10|. 

 7.2, " 3.2 " " 9i 



It is evident that H. millestriata, which is very constant in the 

 mountains, varies in size, proportions and sculpture in the different 

 ecologic conditions of the lower, more arid mesa. 



ZONITID^. 

 Vitrea indentata umbilicata Ckll. 



Dragoon Mountains: Stations 1, 2, 3, 6, 6^, 7, 10, 11, 15, 18, 25, 

 26, 28, 29, 35; therefore generally distributed, probably wherever 

 snails live, as some of the stations were only hastily examined for 

 the larger shells. 

 Zonitoides arborea (Say). 



Dragoon Mountains: Station 28. 



