54 THE NAUTILUS. 



irregularly pitted as in A. lattrei, and the microscopic spiral 

 striae are more plainly denned. 



The embryonic whorls are dark-colored, almost black. 



Height 42, breadth 40; aperture, length 33, width 18 mm. 



Height 40, breadth 37.5; aperture, length 32, width 20 mm. 



Specimens of exactly this form were collected about twenty 

 years ago at "Rio Negro, Chama," by S. L. Schumo, a mem- 

 ber of the Philadelphia Academy of Natural Sciences. 



Four specimens were brought to the writer by an Indian; one 

 (figured) is in the Academy coll., one in coll. of Mr. Bryant 

 Walker, one in the Museum of the Illinois University, and the 

 writer has the other. 



PACHYCHEILUS POTTSIANUS n. sp. 



Shell pyramidal, solid, smooth, of a dingy olive color; whorls 

 eight, hardly convex, a light shade below the suture, the last 

 slightly and broadly depressed on the upper part, in front of 

 the aperture the periphery is obtusely angular, the angle dimin- 

 ishes with the growth of the whorl until the last of the body 

 whorl is broadly rounded. Suture shallow, distinct. Aperture 

 ovate, angular above, circular below, chocolate-colored within, 

 parietal callus well defined and much thickened above, labium 

 slightly thickened. Operculum ovate, nucleus depressed. 

 When the mollusk is in its natural position the shell as viewed 

 from above has the appearance of the penult whorl being 

 humped and the under side of the shell is nearly always eroded 

 as if it had been worn away in moving about. Four specimens 

 measure: 



Length 44, width 17. Aperture, length 14, width 8 mm. 



Length 41, width 17. Aperture, length 14, width 8 mm. 



Length 40, width 16. Aperture, length 15, width 1\ mm. 



Length 42, width 17. Aperture, length 14, width 8 mm. 



This species was taken from two rills on hillsides, in dense 

 woods. Often there was only enough moisture to keep the 

 shells damp, or they were under fallen leaves; with them where 

 there was a half inch or more of water were P. pyramidaiis, from 

 which they differ in being smaller and without any sculpturing. 

 They are wider than P. indiorum of the same length, and have 



