gametophytes and so fine their state of preservation, that 
it has been possible to compare the life-history of this 
fossil form, stage by stage, with the life-history of living 
species of Selaginella. 
The specimenis referred without hesitation to the ex- 
isting genus, Selaginella. It extends the paleontological 
history of the group to the upper Carboniferous. Its age, 
translated into years, according to the estimates of the 
geologist, is approximately 225 million years. 
None of the other five or six known Paleozoic game- 
tophytes exhibits cellular contents,so this discovery may, 
without over-estimation of the quality of the material, be 
regarded as one of the most marvellous petrifactions thus 
far recognized by paleobotanists. A study of the un- 
touched reproductions in this paper should prove this 
claim. 
Description of the specimen. 
The single specimen known is a typical nodule from 
Mazon Creek, [linois, which was collected by Frederick 
QO. Thompson. The only plant fragment in the nodule, 
in addition to the strobilus, is a small unidentifiable frag- 
ment of stem. The strobilus is 27 mm. long, 38.5 mm. 
wide at its greatest width, and showed 84 sporangia, each 
containing four spores. The sporangia vary from 1.6 to 
2.2 mm. in width. The strobilus is slightly curved, but 
it is not possible to determine whether the curvature was 
formed in life or during the process of petrifaction. 
Methods employed. 
The specimen contains megaspores which are visible 
to the naked eye (without ornamentation the spores at- 
tain a diameter of 0.6 mm.). These spores, which are 
brown in color, are infiltrated with calcium carbonate and 
iron carbonate (siderite). Minute crystals of pyrite (iron 
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