382 PROCEEDINGS OF THE ACADEMY OF [May, 



The irregular apertural thickening, lumps, and uneven "teeth" of 

 some forms of M. levis and others show the unfavorable action of 

 extreme aridity.^ 



The apparent absence of Helicidse on the comparatively well- 

 watered southern end of the peninsula is an anomaly. I cannot 

 help thinking that further search will bring some Helices to light. 

 It is a region of fine Bulimuli. 



In the northeastern part of the peninsula and on the Coronado 

 Islands, Micrarionta stearnsiana Gabb is found.^ Farther down and 

 inland the closely related M. orcutti Dall occurs. This seems to be 

 constant in its divergence from stearnsiana in the large lot I have 

 seen. Far off shore on Guadalupe Island is the small M. guadalu- 

 piana Dall, a perfectly distinct species of the typical group of Micra- 

 rionta. 



On the sierra running down the peninsula near the eastern border 

 there are several Sonorella-Wke species, such as Helix lohrii Gabb, 

 unknown anatomically, but probably belonging to the desert group 

 of Micrarionta characteristic of southwestern Arizona and south- 

 eastern California. 



Micrarionta consists of three rather sharply differentiated groups 

 or sections: (1) Micrarionta typical, small, compact shells with the 

 lip strongly reflexed, insular in distribution, M. rujicincta, gabhi, 

 facta, guadalupiana. (2) Section Eremarionta for M. desertorum 

 P. & F., includes also M. hutsoni Clapp and probably all the Cali- 

 fornian and Lower Californian species which have been referred to 

 Sonorella. The lip is expanded, shell smooth. (3) Section Xerarionta 

 for the capacious forms with the lip not expanded or but slightly so, 

 the axis perforate or closed, the shell generally variegated, many- 

 banded. M. veatchii may be taken as the type of this group, which 

 extends from the Channel Islands of California to Magdalena Bay, 

 on the islands and adjacent shore. 



Micrarionta pandoras (Forbes). PI. XV, figs. 17 to 23. 



Helix pandorce Forbes, P. Z. S., 1850, p. 55, pi. 9, f. 3 a, b. Binney, Land 



and Fresh-water Shells of N. A. I, p. 179. 

 Epiphragmophora pandorce (Forbes), Dall, Proc. A. N. S. Phila., 1900, p. 101. 

 Helix damascenus Gould, Proc. Boston Soc. N. H., VI, p. 11, 1856; Otia 



Conch, p. 219. 

 Epiphragmophora pandorce bonitosensis Pils., Proc. A. N. S. Phila., 1898, p. 70, 



pi. 1. figs. 4, 5 (genitalia). 



This species was collected by H. M. S. Herald or Pandora, the 



2 Cf. DaU, "On Insular Land Snail Faunas. " 



3 This has been shown by Mr. G. H. Clapp to differ specifically from M. kelletti 

 of the Channel Islands. 



