6 



THE NAUTILUS. 



sented in this genus, the one with an elevated and the other 

 with a depressed shell. 



Section Rhodacmea, s. s. 



Shell elevated. Radula with a unicuspid central, which has 

 the base triangularly expanded; laterals with the cusp of the 

 mesocone extending but little beyond the base and not over- 

 lapping the base of the central tooth. 



Type, Ancylus filosus Conrad. 



I. Rhodacmea filosa (Conrad). 



Ancylus filosa Conrad, F. W. Shells, 1834, p. 57. 



When I wrote of this species in 1904, (Naut., XVIII, p. 75) 

 I had not seen any specimens from the Black Warrior River, 

 Conrad's original locality. The specimens then before me as 

 was stated, were not typical in that they lacked the "numerous, 

 radiating, prominent lines" described by Conrad. Since that 

 time a considerable amount of additional material has been 

 received from Mr. H. H. Smith, which fully confirms the origi- 

 nal diagnosis. One set from the Black Rock Shoals of the 

 Black Warrior River are rather thin, of a light translucent green 

 color with the apex tinged with rose and are very strongly radi- 

 ately striate, the ribs extending from the apex to the periphery. 

 The largest specimen measures 4.25 x 3 x 2 mm. These shells 

 are undoubtedly typical. 



Similar specimens are before me from the Coosa River from 

 several localities, viz., two miles above Coosa Valley, St. Clair 

 Co.; Ten Island Shoal near Lock no. 2; Leota Shoal; Three 

 Island Shoal, Wilsonville, Shelby Co.; and Vincent Shoal, two 

 miles above Upper Clear Creek. Also from Tallassahatchee 

 Creek, four miles east of Childersburg; Beaver Creek at Greens- 

 port and Canoe Creek. 



All the shells from these localities are quite typical in form, 

 but are uniformly thicker and more heavily striated than the 

 Black Warrior specimens. This heavily striated form seems to 

 be the characteristic expression of the species in the Coosa and 

 its tributaries. The Cahawba River specimens from Lewis and 

 Call mentioned in my former paper, while lacking the strong 



