VAN ESELTINE—SELAGINELLA RUPESTRIS ALLIES. 161 
prostrate plants the megasporangia often occur only on the ventral 
side of the spike, while the microsporangia occur on the dorsal side. 
The megasporangia, normally containing 4 megaspores, are irreg- 
ularly spherical, bulging considerably over each megaspore. The 
megaspores are nearly spherical, but are slightly pyramidal on the 
commissural face, i. e., the side of contact with the other megaspores. 
This face usually bears 3 commissural ridges spreading at approxi- 
mately equal angles from each other, beginning at the apex of the 
commissural side and extending to the base of the flattened portion. 
The ends of these ridges are sometimes connected by a raised ring. 
The surface may be either plain, somewhat rugose, tuberculate, or 
reticulate, wholly or in part. These irregularities on the surface of 
the megaspores are of considerable value in classification. It often 
happens that one megaspore of the tetrad develops at the expense of 
the other three, which are then much dwarfed. The stated size of 
megaspores in the following descriptions is that of an average nor- 
mal megaspore. 
The microsporangia are reniform, and contain several hundred 
microspores. These present much the same general appearance as 
the megaspores, but are exceedingly minute. 
The writer’s heartiest thanks are due to Miss Kathryn Steinle, of 
the Western High School, Washington, D. C., for the drawings of 
leaves, sporophylls, and megaspores. 
DESCRIPTIONS OF SPECIES. 
KEY TO THE SPECIES. 
Megaspores smooth, at least on the outer face. 
Stems (including leaves) up to 1 mm. thick; leaves 
without cilia in the dorsal suture, bearing a 
cluster of cilia on the long adnate base_-_----- 2. S. arenicola. 
Stems thicker; leaves usually bearing 4 to 10 cilia in 
the dorsal suture, without a cluster of cilia at 
the base. 
Plants 7 to 12 cm. high; megaspores merely rugose 
on the commissural face. 
Leaves rather lax, glaucous green ; dorsal cilia 
of leaves as large as the marginal_____ 3. S. humifusa, 
Leaves closely appressed, darker green; dor- 
sal cilia, when present, minute and usu- 
ally confined to the basal portion of the 
dorsal suture ____-------------------- 4, 8. funiformis. 
Plants 3 to 6 cm. high; megaspores rugose-tubercu- 
late on the commissural face___----------- 5. S. acanthonota. 
Megaspores alveolate or rugose-reticulate or rugose-tuber- 
culate. 
Sete tortuous; plants prostrate or ascending; mega- 
spores rugose-tuberculate. 
Plants prostrate, spreading; leaves 8-ranked__--- 6. S. tortipila. 
Plants ascending, densely cespitose; leaves 13- 
ranked____________--_--_------------------ 7. S. sherwoodit. 
