184 THE NAUTILUS. 



A NEW MICHARIONTA FROM ARIZONA. 



BY H. A. PILSBRT AND .1. H. FERRISS. 



When at the Grand Canyon of the Colorado in the autumn of 

 1906 the writers met Mr. W. J. Gilchrist, who at that time was about 

 to leave the Canyon for the mining region of the lower Colorado. Be- 

 sides various friendly and helpful services in connection with our 

 work at the Canyon, Mr. Gilchrist volunteered to look out for snails 

 in the region he was about to visit. It was with a great deal of 

 pleasure that one of us received a letter and package of snails, making 

 good his offer of assistance. 



In that desert country snails are not common, and for a long 

 time none were found. Finally, Mr. Gilchrist writes, " I was build- 

 ing a stone monument on a mining claim just after a heavy rain and 

 found three live snails on a rock. These and four dead ones were 

 all I have been able to find. They came from a small range of 

 mountains 12 miles south from Parker, Yuma Co., Arizona." 



The snails prove to be of a new species, which may be described 

 as follows. 



MICRARIONTA DESERTORUM n. sp. Plate xi, figs. 6-10. 



The shell is small, depressed, openly umbilicate, the width of 

 umbilicus contained nearly 5 times in that of the shell, glossy, opaque, 

 pinkish-white with some oblique streaks of flesh-color, and sometimes 

 a few corneous dots ; the inner 2^ whorls fleshy-corneous. The 

 spire is convex but very low, whorls about 4^, the inner ones rather 

 slowly increasing, the last much wider, about double the width of the 

 preceding. The embryonic shell consists of l whorls, the first 

 fourth of a whorl smooth, the rest with close, even sculpture of min- 

 ute papillae, which are lengthened in a direction parallel to the 

 sutures, and form a regular pattern of oblique, forwardly descending 

 and ascending rows. The post-embryonic whorls have fine, irregu- 

 lar, somewhat wavy striae in the direction of growth-lines, and papillae 

 like those of the embryonic whorls but much more sparsely placed, 

 and disappearing near the end of the penultimate whorl. The last 

 whorl has weak growth-lines only. It is rounded periferally and 

 descends slowly to the aperture. The suture is deeply impressed, 

 especially at the last whorl. The aperture is oblique, rounded-oval. 



