SPIROSTEMMA. 285 



3 1/2 whorls, weakly ribbed vertically, the last smoother, the 

 line of union with the after-growth distinct (Vol. XVI, pi. 

 11, fig. 89, S. inusitata). 



The teeth of the radula are very numerous and extremely 

 minute, placed in V-shaped rows. The central tooth in each 

 row is very narrow, with a denticulate or serrate cusp, smaller 

 than the ectocones of the lateral teeth. The lateral teeth have 

 the mesocone expanded, with a straightly truncate, closely 

 serrate cutting edge; ectocone smaller, with the edge serrate 

 or nearly smooth. All of the side teeth are of substantially 

 the same shape, and they are very numerous, the count exceed- 

 ing 50.1.50. 



fin 8. princeps (pi. 43, fig. 10, a group of four laterals) the 

 ectocones are rather long, narrow and smooth on the inner 

 teeth, bifid on the outer (fig. 9). In S. inusitata from Swift 

 River (pi. 43, figs. 11, 12) the central tooth has a single notch 

 in the cusp, and the adjacent marginal teeth have simple, 

 conic, short ectocones; the lateral teeth farther out (fig. 11) 

 have the ectocones serrate. In S. tenella from west of Ocho 

 Rios the teeth are decidedly smaller, narrow and crowded, 

 with the cusps subterminal on the basal-plates, and all are 

 serrate (pi. 43, fig. 13).] 



Jaw and soft anatomy unknown. The shells are illustrated 

 on plates 34a to 37 ; the teeth on pi. 43, figs. 9 to 13. 



The specimen I figured in 1898 as " U. rubra," for the type 

 of this genus is not that species, but S. inusitata Vendr. 



In its most advanced type, represented by U. tenella and 

 allied species, the axis is like a cork-screw, or a spiral stair- 

 way around a central well, which may be seen on looking into 

 the aperture from below. In the group of U. princeps, the 

 central hole may still usually be seen, though smaller. In 

 U. dunkeri the axis is hardly spiral beyond the last whorl. As 

 in other Urocoptina the axis is a solid style. 



This genus is closely related to Anoma, which has the same 



>e of teeth ; but in Anoma the peristome is not continuous 



>ve, the aperture being truncate there ; the shell is more or 

 swollen, instead of being pillar-shaped, and it is glossy, 

 illy more or less variegated or bright-colored; moreover, 



