462 Ganong . — The Comparative Morphology of 
trace of rib-formation. I have not observed the beginning 
of the splitting of the vegetative points on the tubercles, but 
no doubt it comes about there precisely as in E. Scheerii. 
M. radiosa neo-mexicana belongs also with the grooved 
forms ; its cotyledons (Fig. 46) are pointed, a feature very 
rare in this genus, but their small size would prevent any 
confusion of this with a small Echinocactus. 
In the furrowless division occur the smallest embryos, and 
of the several species I have studied all are much alike. As 
shown by M. Goodridgii and Sempevvivi the hypocotyl is 
very swollen, larger above the middle and with small rounded 
cotyledons. In the development of the epicotyl in this 
division I have not yet determined the very important point 
of the exact mode of appearance of the vegetative point 
which in the adults stands in the axils of the tubercles and 
produces the flowers. Theoretically this ought to appear as 
it does in the furrowed Echinocacti and furrowed Mamillariae, 
i. e. the point which on the first formed tubercles is single 
should on some of the later become stretched out, and in still 
later ones the stretching should go yet farther so as to 
separate it into two parts, and so on, the stretching taking 
place at earlier and earlier stages in the growth of the 
mamilla until finally it occurs before this has become raised 
from the main stem. 
17. Genus Anhalonium. 
A. Jissuralum, Engelm. Figure 49; also in Goebel, PI. II, Fig. 7. 
A. prismaticum, Lem. Figure 50. 
This small, but morphologically very important, genus 
contains only small somewhat Mamillaria- like forms with 
angular tubercles and no visible spines. They are flattened 
above and in shape like a top with the greater part buried 
in the earth. The tubercles show two types, one with a 
furrow and one without, in this showing parallelism with 
Mamillaria. 
Important though this genus is, but a single good figure 
