Occasional Papers of the Museum of Zoology 53 
tions (example G. calverti Pilsbry) will be found to belong to 
any of these groups in its strict sense. 
In the radulae examined of these three groups, Guppya, 
Habroconus, and Fuconulus, three more or less distinct ten- 
dencies or trends seem to be present. 
1. A’tendency for all of the teeth to become elongate and 
for the outer teeth to turn inward and to lose the ectones. The 
marginals of all three groups have lost the ectones, but the 
central and laterals of Guppya s. s. have not been affected to 
any great extent. Both the centrals and the laterals of the 
other two groups are elongated, although in Habroconus this 
is accomplished by the increase in size of the distal portion of 
the reflected edge, while in Euconulus the cusps themselves 
have been lengthened to a greater degree. The laterals of 
beth of the last two groups show a progressive tendency, from 
the center out, for the ectocones to move up on the outside of 
the mesoccnes and finally to diminish in size. 
2. A tendency for the ectocones to be reduced in numbers. 
This has not affected Guppya s. s. as much as the others, as all 
_ of the marginals have at least two ectocones. Half of the well- 
developed marginals of Habroconus still retain two ectocones, 
while none of the large marginals of Euconulus have more 
than one. The bicuspid teeth tend to move back into a less 
oblique position than that of the tricuspid. This tendency 
towards reduction of the number of cusps on the marginals 
is carried still further in such genera as Zonitoides, where the 
definitive marginals are mostly unicuspid. 
3. A separate tendency, at least somewhat coincident with 
size, to reduce the number of teeth in the transverse rows. 
Thus, the largest species, G. trochulina, has about 119, E. ful- 
vus about 77, &. elegantulus about 85, G. gundlachi 65, and G. 
sterki 41. Up to a certain point, this appears to go on more 
