UROCOPTIS. Ill 



are 9.1.9 teeth. In U. elliotti Fischer found 14.1.14 teeth. 

 They decrease rather rapidly in size towards the edges of the 

 ribbon, as in Idiostemma. 



In the section Tomelasmus, U. sauvalleana has 20.1.20 

 teeth, very regular and slowly decreasing towards the edges 

 of the radula, much as in typical Urocoptis. 



U. pruinosus (pi. 61, fig. 15) has 12.1.12 teeth, not mate- 

 rially unlike those of U. elegans, but the cusps are a little 

 narrowed, as in U. dautzenbergiana. 



In U. ventricosa (pi. 60, figs. 5, 6, 10) the formula is 

 9.1.9. Teeth formed as in pruinosus, but of course decreasing 

 more rapidly. 



In the slender, long, Brachypodella-like U. wrighti of east- 

 ern Cuba (pi. 61, fig. 12) there are 9.1.9 teeth, shaped like 

 those of U. ventricosa except that the outer ones are more 

 oblique and shorter. In U. baculum (pi. 60, fig. 11) the ra- 

 dula is even narrower, teeth 7.1.7, the two outer on each side 

 rudimentary and very oblique, and there is a somewhat abrupt 

 decrease from the second to the third lateral, to some degree 

 approaching the condition of the less modified forms of 

 Brachypodella. The centrals are rather wide, as usual in 

 Gongylostoma. Further notes on the teeth of slender species 

 may be found under Cochlodinella and Tomelasmus (pi. 63). 



From the above it will be seen that the greatest modifica- 

 tion of the radula is found in Idiostemma, Callonia and cer- 

 tain species placed in Tomelasmus, such as U. ventricosa and 

 U. ~baculum. In these forms there has been extensive reduction 

 in the number of teeth in a transverse row. This reduction 

 is not correlated with, either a particular shell-contour or 

 axial sculpture, though it accompanies, in most cases, highly 

 evolved and variously aberrant shells. The several forms 

 in which the tooth-formula has been specialized by reduction 

 are not closely related. The tooth-reduction must be looked 

 upon as a secondary modification undergone by several phyla. 



The central tooth is very narrow in the Jamaican subgenus 

 Urocoptis; rather narrow in Idiostemma, and comparatively 

 wide in the subgenera Gongylostoma, Cochlodinella and Auto- 

 coptis. 



