76 THK NAUTILUS. 



amples seen are two lots in the Lewis collection, so labelled by liim, 

 one from the Coosa and the other from the Cahawba River, Ala., 

 and a set from the latter stream collected by Call. Dr. Pilsbry has 

 kindly compared these with tlie type specimen in the collection of 

 the Academy and writes that though less strongly striated radially, 

 " they agree with the type in form, and the almost invariably red 

 apex." 



As evidenced by these shells. A.Jilosus closely resembles in sliape 

 and contour the eastern form of A. tardus. It differs, however, in 

 the light green color, the radiating ribs and, when present, the rosy 

 apex. In none of these shells are the ribs very strongly developed, 

 nor do they extend uniformly over the shell from apex to periphery. 

 But there are indications of them on all. They are usually more 

 conspicuous on the sides, especially immediately below the apex and 

 toward the anterior slope, the central portion of the side slope being 

 comparatively smooth. Between these heavier ribs are usually 

 several smaller ones, which seem to be extensions of the apical 

 striae. The larger ribs are heavier and coarser than those noticed in 

 any other species and, when fully developed, would be " very promi- 

 nent " and conspicuous. The anterior slope is usually strongly con- 

 vex, although, as shown by the figures, there is some variation in 

 this particular; the posterior slope is nearly straight and direct, not 

 very oblique, and the side slopes are slightly convex. The marginal 

 outline varies from a regular oval to obovate with the greatest width 

 behind the apex. 



The Cahawba River specimens are thinner and more translucent 

 than those from the Coosa and are apparently less typical, being less 

 elevated, with tiie anterior slope more oblique. 



The apex is much eroded in all of the Coosa specimens, but is 

 nearly perfect in those from the Cahawba. When perfect it is 

 " somewhat inclined " or rather flattened posteriorly, and very 

 slightly inclined to the right. Binney and Tryon are consequently 

 in error in referring the species to Acroloxus ( Velletia), which is a 

 European group not represented in our fauna. 



The dimensions of the specimens figured are as follows : 



Fig. 1, length 4.0, breadth 2.9. alt. 1.9 mm. 



Fig. 4, length 4.5, breadth 3.5, alt. 2 mm. 



Fig. 7, length 4.0, breadth 3.0, alt. 1.75 mm. 



