66 PROCEEDINGS OF THE ACADEMY OF [Feb. 



4^, rather slowly widening to the last, which is nearly double the 

 width of the preceding, and well rounded peripherally. The embryonic 

 shell consists of U whorls; the apex is smoothish; then a radially 

 wrinkled area follows to the end of the first half whorl; the next 

 whorl has forwardly descending delicate threads on its outer or per- 

 ipheral half, the inner half being irregularly, shallowly pitted and 

 roughened. The succeeding neanic whorls are lightly striate obliquely 

 and very slightly, minutely roughened. The last whorl descends 

 rather deeply in front . The umbilicus is contained about 5h times in the 

 diameter of the shell. The aperture is very oblique, peristome expand- 

 ed, the ends strongly converging, the columellar end dilated, slightly 

 impinging on the umbilicus. 



Measurements of seven specimens were given in our former paper, 

 with diameters of 15 to 17.8 mm. Sixty-nine adults taken in 1906 

 have the following diameter- : 



'r-> 



Diam. in mm 15 15.5 15.8 16 16.2 16.3 



No. of shells 4 3 2 22 2 7 



Diam. in mm 16.5 16.7 16.8 17 17.8 18 



No. of shells 5 4 6 12 1 1 



About 84 per cent, are from 16 to 17 mm. in diameter, and the 

 total range in diameter is only 3 mm. 18 Otherwise variation is seen 

 only to a very slight extent in the width and intensity of the band 

 and in the degree of deflection at the aperture. 



Type locality. — Quartzite Hill, back of Dixon's place, about a mile 

 south of old Fort Bowie. It has been found nowhere else. 



The locality was wrongly given as "Bowie" in our former paper. 

 Bowie is a station on the S. P. Railway about 15 miles from Fort 

 Bowie, and on the mesa where no snails live. Fort Bowie is now 

 deserted, and only the roofless adobe buildings and the cemetery 

 remain. 



Sonorella bowiensis was found only in one colony very limited in 

 extent but prolific in individuals. This colony — the only place where 

 we have ever found Sonorella in abundance — is in a small thicket of 

 long-leaved scrub-oaks with some underbrush of service berries 

 (Amelanchier sp.) under a low cliff, somewhat more than half way to 



18 The concentration around the diameters 16 and 17 mm. is partly due to 

 the fact that all shells more than 15.8 and less than 16.2 were counted as 16, 

 and similarly with 17, giving a wider range than with any intermediate measure- 

 ments. 



