1910.] NATURAL SCIENCES OF PHILADELPHIA. | 71 
Creek, at an elevation of about 6,000 feet. These small specimens 
- contrast with those from Stations 13, from shaded slopes, where the 
mode is at 20 to 20.5 mm., and the range from 17.75 to 21 mm. _Large 
shells occur at Station 11, at the shaded and humid base of Ried’s 
Mountain, about 6,000 feet elevation, and at the head of Pine Canyon, 
at about 8,000 feet, also in a comparatively humid and well-shaded 
situation. The shells from other places, while too few to be worth 
tabulating, or to give reliable curves, support the above conclusions 
as far as they go. 
Diameter in Head 
mm. Sta. 1., Sta.4. Sta. 11. ‘Sta.12. Sta.13 Pine Canyon. 
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The sole, in alcoholic examples, is yellowish in the central field, the 
lateral areas grayish, grooves rather indistinct. The back is blackish, 
sides pale. 
Specimens from numerous lots were dissected, genitalia of two 
being figured (pl. V. fig. 6, No. 94,335 from Station 13, South Fork of 
Cave Creek, and fig. 4, No. 94,332, from Station 11, Cave Creek). The 
penis is longer than in the original type specimen, but in about the 
same proportion to the length of the vagina, which varies considerably. 
This difference in length is perhaps due to the different modes of 
preservation. The basal sheath of the penis and its retractor are 
both quite short. The arcuate shape of the penis is due to its position 
near the periphery of the last whorl when the animal is retracted. 
