With the exception of S. campestris, the species of Stenopadus, as exemplified
by S. chimantensis fig. 90 A, B), have the following characters in common.
The grains have an elliptic outline, this shape being described by Erdtman (1952)
as subprolate for those of narrower shape, or prolate sphaeroidal for those approaching
more nearly a sphaeroidal form. The outer ektexine is virtually smooth
(psilate), the spinulose emergences being one micron or less high. Stenopadus
campestris (fig. 89 A, B) shows a sphaeroidal shape, with minute spines (spinulose)
somewhat larger than those in the other species. All species of Stenopadus
show a relatively thin exine, approximately 3 to 5 microns in thickness.