THE NAUTILUS. 77 



ehell measured is 3^x 1^ mm. with about 5^ whorls, and the largest 

 4-J- X 2 mm. with 6| whorls. Internally there is a strong lamella on 

 the columella, which can only be seen by breaking the shell, about 2 

 whorls long in fully adult shells. Examination of a large number of 

 ehells of all ages shows that this lamella is a mark of maturity, as it 

 does not appear until after the angular, parietal and outer columellar 

 lamellae have begun to form. 



The arrangement and number of the other lamellae and plicae are 

 the same as in the type, with the usual variation as to extra denticles, 

 ordinarily seen in Bifidaria. The body whorl is decidedly angular at 

 the umbilicus, and flattened below the periphery. 



Foothills of the Plumosa Range, about eight miles east of Quartz- 

 site, Yuma county, Arizona, in drift. Collected by Mr. Geo. S. 

 Hutson. 



Type No. 5769 of my collection. Cotypes in Academy Natural 

 Sciences, Philadelphia, and U. S. National Museum. 



In the peck or more of drift from which these shells were picked, 

 there were only two other species, Bifidaria hordeacella Pils. and 

 Pupoides marginatus (Say), with not even a fragment of anything 

 else. 



In the Eagle Tail Mountains, twelve miles north of Kofa, Yuma 

 county, at an altitude of about 2,000 feet, Mr. Hutson found a form 

 which is apparently intermediate between the type and intuscostata, 

 in that the columellar lamella is weaker and does not extend in so 

 far. This is probably the form referred to by Pilsbry in Proc. 

 A. N. S., 1906, page 146, taken by the late Dr. Ashmun at Temp6, 

 Maricopa county. The habitat given by Hutson is : " In moist 

 places among piles of loose rock covered by decaying cactus. Asso- 

 ciated with these were also Bif. hordeacella and P. marginatus. 



The finding of this species in Cochise, Maricopa and Yuma 

 counties, shows a distribution of B. tuba clear across the territory. 



ASHMCNELLA KOCHII D. sp. 



Shell very much depressed, almost flat above, convex below, car- 

 inated, the carina about in the plane of the upper surface ; sutures 

 well impressed, whorls 5-^; surface almost smooth, with faint and 

 closely-set incremental lines ; nuclear whorl and a half finely granu- 

 lated ; base convex, flattened around the umbilical region ; umbilicus 

 deep, about 1^ mm. wide, showing a full turn of the penultimate 



