FOSSIL PLANTS. 83 
coriaceous or horny texture shining on the surface. * * * The rhizoma is 1.20 to 
1.50 m. long, perfectly cylindrical, 55 to 4 cm. in diameter, simple and regular in its 
whole length, with a rough surface. * * * The top of the rhizoma, abruptly en- 
larged into a globular shape resembling a cabbage head 17 cm, in diameter, looked, 
when broken, like a convolute undeveloped frond, with branches densely rolled to- 
gether into a ball where the divisions or the relative disposition of the branches could 
not be distinctly observed. The fronds, very large, 1 to 1.25 m. long by 50 cm. broad, 
are composed of cylindrical divisions, the primary and secondary ones being thick, 
the larger 2 cm. in diameter, flattened on the surface, all gradually smaller from the 
base to their ends, closely distichous, dichotomous, flexuous, with oblique multiple 
subdivisions, the ultimate two-ranked being very closely pinnately distichous, eylin- 
drical, pointed, or gradually narrowing from the middle and effaced at the apex. 
I have copied this description nearly entire because it is almost. liter- 
ally applicable to a plant represented on Pl. XXI of this memoir and ob- 
tained from the sandstones of Portland, Conn. When we consider the vast 
interval of time between the deposition of the Umbral shale of Pemsyl- 
vania and that of the Rheetic sandstone of Connecticut, one the base of 
the Carboniferous system and the other the summit of the Trias, it can 
not fail to be regarded as interesting and surprising that the resemblance 
should be so complete. But for the a priori improbability that a species of 
sea-weed should be so long-lived I should hardly feel justified in giving 
even a new specific name to the Triassic specimens. Possibly a comparison 
of more material would show differences not now perceptible, but the pecu- 
liar mode of growth and the details of structure seem to be essentially the 
same. In the Portland sandstones, as in the Umbral shales, the fronds of 
Dendrophycus are enrolled in masses that suggest cabbage-heads of large 
size and rather loose texture, while the mode of subdivision and the char- 
acter of the final ramifications of the frond are so like that, with the simi- 
larity of the inclosing rock, the specimens from the two localities and 
horizons are almost undistinguishable. Though a less conspicuous example 
of a “persistent type” than Strophomena rhomboidalis or Atrypa reticularis 
the survival of a sea-weed of such strongly marked character through so 
great an interval is as unexpected as it is interesting. 
Spirophyton, which begins in the middle Devonian (Corniferous) and 
runs up into the Coal Measures, is another example of persistence in an allied 
group of algze; but that genus is represented at the different horizons by 
