186 PROCEEDINGS OF THE ACADEMY OF [March. 



Alt. 9.5, cliam. 18.3 mm. 

 " 10.2, " 17.0 " 

 " 8.0, " 16.0 " 

 " 9.8, " 16.0 " 



This race occupies the same zone as 0. y. extremitatis in the Kaibab 

 limestone. The stations are about 20 miles apart, but including the 

 windings of the canyon, as the snail travels, the distance would be 

 far greater. The embryonic stage is very much alike in O. y. profun- 

 dorum, extremitatis and angelica, but the neanic and adult stages 

 differ. 



Cotypes No. 103.239 A. N. S. P.. collected by Pilsbry and Ferriss, 

 1906. 



Oreohelix strigosa depressa (Ckll.). Pis. XIII, XIV. 



[Patula strigosa] var. Cooperi Binnev, Manual Amer. L. Shells, p. 166, fig. 



153 (teste Ckll.). 

 Patula strigosa cooperi var. depressa Ckll., Nautilus, III, p. 102, January, 



1890, canyon near Durango, Colo. 

 Oreohelix strigosa Gld., Pilsbry, Proc. A. N. S. Phila., 1905, p. 272, pi. XXV, 



figs. 45-47 (shell); pi. XI, figs. 14, 15 (embryonic shell); pi. XIX, fig. 3 



(genitalia); pi. XXII, figs. 1-3 (teeth); pi. XXIII, fig. 25 (jaw). 



New Mexican examples of O. s. depressa have been fully described 

 and figured in a former paper of this series. In the country north of 

 the Grand Canyon it is an abundant snail, varying widely in size, 

 form, color, and to a less degree in sculpture not only in different 

 colonies, but frequently among individuals of one colony. 



In some districts, as along the western escarpment of Powell Plateau, 

 there is a marked tendency to lose the dark bands. In some other 

 places beautiful albino shells occur in colonies composed chiefly of 

 well-colored shells. There is a tendency in many places to produce 

 more compactly coiled shells than typical depressa, the spire being 

 higher and the total diameter and the umbilicus smaller in some of the 

 shells. This culminates in a form of shell which is not distinguishable 

 from O. cooperi, found in a few stations. 



In some arid situations, especially the head of Quaking Asp Canyon, 

 the shells 'are conspicuously dwarfed, their development arrested. 

 No colonies are markedly gerontic, though in a few there is a tendency 

 towards senile characteristics in occasional individuals. 



The spiral sculpture is generally distinctly developed, and some- 

 times some larger, widely spaced spirals can be seen on the base of the 

 shell. 



Specimens are illustrated on Plates XIII and XIV. Some 



