118 PROCEEDINGS OF THE ACADEMY OF [Feb., 



but in other individuals of the same colony it may be small or barely 

 observable, so that the series from a strong lamella to none is prac- 

 tically a continuous one in some colonies, though usually this lamella 

 is either distinctly developed or wholly wanting. The same statement 

 applies to the basal lamella, except that it is never very large and 

 usually quite small and short when present. 



The study of these races is extremely complex, and we have been 

 unable to find time to enter upon it seriously. Any full record of a 

 form should take into account the number of ribs on a whorl or their 

 distance apart, as well as the proportions of the shell, number of whorls, 

 length of cone, and the lamellae. 



(a) In many colonies a longer and a shorter form may be selected, 

 with only few intergrading specimens; and there may also be a notice- 

 able difference in sculpture. Such colonies may perhaps be hybrid, 

 composed of two incipient races. (6) Different colonies in the same 

 district, often living under apparently identical conditions, and 

 frequently in close proximity, may show differences in size, ribbing or 

 comparative frequency of certain combinations of lamella?, in fact, 

 incipient racial divergence. The mingling of two or more such colonies 

 by their spread, aided by changing conditions of surface, may have 

 given rise to colonies of the (a) type. 



In some cases, where the colonies are widely separated, they have 

 apparently evolved into reasonably distinct subspecies, probably 

 in the alienee of int emigration. The Cave Creek colonies of H. 

 chiricahuana illustrate this. 



Holospira arizonensis Steams. PI. XI, figs. 1-4. 



H. arizonensis Stearns, Proc. U. S. Nat. Mus., XIII, 1890, p. 208, pi. 15, 

 figs. 2, 3 (Cave at Dos Cabezas). Bartsch, Proc. U. S. Nat. Mus., Vol. 

 31, 1906, p. 134. 



This species has hitherto been known by fourteen fragments and 

 one perfect specimen, the type No. 104,392 U. S. N. M. It measures, 

 length 12.S, diam. at 10th whorl 4.2 mm., whorls 12. We did not 

 visit Dos Cabezas Cave, but our guide and driver, Mort Wien. passed 

 there and collected a series of shells from close to, almost in, the mouth 

 of the cave. 24 Fresh shells are pale corneous brown, glossy, bluish 

 and subtransparent in places on the intermediate whorls. First 2\ 

 whorls smooth; following 6 whorls sharply striate, the striation grad- 

 ually disappearing, so that two or three whorls preceding the last are 

 smoothish. The last whorl is dull, coarsely striate, its outer wall 



24 It is stated that Mr. Vernon Bailey collected the types in the cave. They 

 had doubtless been carried there by wind or mice. This accounts for the broken 

 condition of all but one specimen of the type lot. No Arizonian Holospira 

 lives in caves or shaded or damp places. They live in dry and sunny situations. 



