1910.] NATURAL SCIENCES OF PHILADELPHIA. 117 



8,000 feet, Pine Canyon, 7,500 feet, and " Box" of Rucker Canyon. It- 

 has been listed by Dall from Fly's Park. 



While not strongly differentiated, adult shells of this race are readily 

 distinguishable. The aperture clasps the preceding whorl less deeply 

 than in ingersolli. The microscopic spiral striation also is somewhat 

 better developed in the examples compared. 



Thysanophora ingersolli convexior (Ancey). Fig. 24, G, H, I. 



Microphysa ingersolli var. convexior Ancey, Conchol. Exch. II, p. 64, Nov., 



1887 (Logan Canyon, Utah). 



"Shell a little smaller; spire scarcely planulate, the apex not sub- 

 immersed, distinctly convex; whorls 5, not 5£, regularly but less 

 slowly increasing, umbilicus smaller" (Ancey). 



This form has not been figured. We have seen no topotypes, but 

 examples from Weston, in eastern Oregon, collected by Henry Hemp- 

 hill, evidently belong to the same race. One of these is figured (fig. 

 24, g, h, i). The specimen figured measures, alt. 2.5, diam 4.8, width 

 of umbilicus 1 mm., whorls 5f. The aperture is a little wider than 

 in typical ingersolli. 



Family UROCOPTID^J Pils. 



Genus H0L0SPIRA von Martens. 



All of the Holospiras now known from Arizona belong to a single 

 group of closely related species, characterized by the light brown 

 shell, having a stout lamella on the axis in the penultimate and first 

 part of the last whorl, often in addition a superior or parietal lamella, 

 and sometimes a basal lamella also. In several of the forms the 

 lamellae vary from one to three, as Ave have demonstrated by cutting 

 from twenty to fifty individuals of a single colony. In colonies so 

 varying, the number of internal lamellae is not correllated with age, 

 size or any other external feature of the shells, so far as we can discover, 

 after collecting and examining hundreds of shells from a great number 

 of colonies. The subgeneric divisions {Eiulistemma, Tristemma) based 

 upon the number of internal lamellae in shells of this type have, there- 

 fore, no basis in nature. While the Arizona species differ somewhat 

 from the Mexican type of the subgenus Bostrichocentrum in texture 

 and sculpture, it does not seem that the differences are of subgeneric 

 importance, and for the present we will place them in that group. 



The variations in the internal lamellae recorded below are really 

 less discontinuous than might be supposed by the tables. The axial 

 lamella is invariably present, but it varies in strength and length. 

 The superior lamella may be very strong and over a half whorl long, 



