30 THE NAUTILUS. 



71 from 11.3 to 13 mm. The smallest have barely 5 whorls. 

 Probably some local condition dwarfs all the individuals in these 

 stations. 



In several stations, 70, 71, 72, 73, there are very beautiful 

 albino specimens of a transparent marguerite-yellow tint among 

 the dark ones. See first two figures within second row, repre- 

 senting an albino and one of the darkest examples, from station 

 72. 



Compared with A. proxima Pils. of the Chiricahua range, this 

 species differs as follows : It is less depressed. The peripheral 

 angle becomes weak and then nearly or quite disappears at the 

 last part of the whorl where it is more swollen above. There is 

 a furrow behind the lip up to the suture, and the upper lip is 

 reflexed, while in A. proxima the upper lip is straight, not ex- 

 panded, and there is a whitish triangular patch and no gutter 

 above the end of the outer lip. A, proxima has one more whorl. 

 The aperture is larger in A. tetrodon when specimens of the 

 same diameter are compared. A. tetrodon is less depressed and 

 less angular than A. pilsbryi, which further differs by its papil- 

 lose surface. 



All of these colonies in the box of Dry Creek Canyon were 

 found in company with Oreohelix barbata Pils. The colonies 

 farther up the stream had also A. mogollonensis for company. 



In color and teeth, A. tetrodon is much the same as the Cave 

 Spring A danielsi, with the addition in this of a parietal lamella. 



Dry Creek is dry at the crossing of the Silver City and 

 Mogollon road. Six miles above it becomes a large and beau- 

 tiful trout stream, boxed in for two miles so closely and roughly 

 that the banks are not used for grazing purposes, and are never 

 disturbed. Twenty snail colonies were found in the rock slides 

 during a hasty search of these, two or three more miles above. 

 Above the box shells were found in the grass and weeds also. 

 In nearly every instance the colonies differed in size and in the 

 character of the teeth. Some had no teeth (var. mermis); 

 others, as with A. heterodon Pils. , of the Huachucas, ran from 

 no teeth to four, with all the variations between (var. mwfator). 



In the colony at Station 60 there are some individuals differ- 

 ing from typical tetrodon by having the parietal tooth reduced 



