98 PROCEEDINGS OF THE ACADEMY OF [Feb., 



Group of Ashmunella proximo. 



From Old Fort Bowie these forms extend southeastward to the end 

 of the Chiricahua range. Northward beyond the depression at the 

 Fort, in the Dos Cabezas end of the range, no Ashmunella has been 

 found. The mountains here are apparently too barren and dry for 

 Ashmunella, though they support the more hardy Sonorellas. 



The colonies seem to be small and widely separated in the area 

 northwestward of White Tail Canyon, but much of that country remains 

 to be explored, especially between Big Emigrant and White Tail 

 Canyons, as well as the entire region of the southwestern watershed. 



A. ferrissi and A. angulata are distinct from the others by their 

 flattened whorls and conspicuously compressed outer basal tooth. 

 The other species are intimately related, and their variations make 

 a complexly branching form-chain. An adequate study of the 

 material in hand, some thousands of shells, would require more ample 

 time than we can give. Since not half of the territory is adequately 

 covered by our series, we must leave full consideration of the subject 

 for another occasion. 



Our knowledge of the forms from Rucker and Horseshoe Canyons 

 and the region around them is still very defective. The forms seem 

 to be related somewhat, as shown in the following diagram : 



proximo. 



emigrans 



lepiderma 



pomeroyi, albicauda — fissidens 



duplicidens 



If a single basal tooth is primitive, then A. duplicidens is the least 

 evolved member of the series and of the whole Chiricahuan group of 

 Ashmunellas. Then A. proxima and lepiderma would be the most 

 evolved. All of the forms with more or less concrescent basal teeth 

 are extremely variable in the degree of union of these teeth. Every 

 colony of fissidens, emigrans, albicauda, pomeroyi and duplicidens 

 shows great individual variation in this respect. There seems to be 

 complete intergradation between the separated basal teeth of proxima 

 and the united teeth or single tooth of fissidens and duplicidens. 

 Ashmunella lepiderma n. sp. PI. VII, figs. 1-7. 



Shell umbilicate, the umbilicus about one-fifth the total diameter 

 of the shell, much depressed, biconvex, acutely carinated peripherally, 



