THE NAUTILUS. 



5 



side teeth, but differs in having them longer and sharper, those 

 of the marginals extending beyond the base. This characteristic 

 difference in the raduJa would seem to definitely establish the 

 generic validity of the group. 



III. Subfamily Rhodacmein^e, n. subf. 



Jaw composed of numerous segmented plates. Radula with 

 a long, slender central, unicuspid or faintly bicuspid, and with 

 the base widely expanded in some species: the first lateral very 

 large with an enormous mesocone, the blade-like cusp extend- 

 ing beyond the base, the ectocone is back of the mesocone, en- 

 tirely separated from it and has several small cusps; there is no 

 endocone. The four laterals are similar in shape but diminish 

 rapidly in size toward the margin, these are succeeded by two 

 or three transition teeth, smaller and with more or less imper- 

 fect cusps. The marginals are very small, rapidly decreasing 

 in size toward the outer edge, with large quadrate bases, wider 

 than high, vestigial, the cusps being nearly, if not quite, 

 obsolete. 



The rows of teeth are more or less V-shaped and with the 

 immense laterals and minute marginals present a remarkable 

 appearence quite unlike any other group belonging to the family. 



Gwatkin, (J. of Con., XIV, 1914, p. 147), has already com- 

 mented upon the resemblance of the radula to that of Brachypo- 

 della. 



All of the species known to belong to this group have the 

 apex of the shell tinged with pink. 



Genus Rhodacmea, n. g. 



Shell patelliform, conical, elevated or depressed, apex tinged 

 with pink. Radula and jaw as in the subfamily. Soft anatomy 

 otherwise unknown. 



Type, Ancylus filosus Conrad. PI. 3, fig. 2. 



The species belonging to this genus are not confined to the 

 Coosa drainage as Gwatkin supposed, but are also found in both 

 the Tennessee and Ohio systems. 



As in Lanx and Ferrissia, two well marked groups are repre- 



