ZS 
geological ages, and somewhat more definite calcareous forms have 
a like range and are particularly abundant in some of the older 
rocks. They resemble the modern coralline or reef-building algae. 
The second transparency shows four early types of algae. 
Cryptozoon, in the lower left corner, represents one of a variety 
of large concentric types, in some cases reaching several feet in 
diameter; they form reef-like masses in the pre-Cambrian and 
older Paleozoic rocks, and have now been found in North America, 
Europe, Asia, Greenland, and Australia. They are believed to be 
related to the blue-green algae, although some authors dispute even 
their organic nature. Supposedly related types are the genera 
IWVeedia, Spongiostroma, Collenia, and others. 
The second restoration, Primicoralling, represents a_ clearly 
marked calcareous form with a hollow jointed axis carrying whorls 
of lateral branches at the nodes. Complete specimens are rare, but 
the detached joints make up masses in the Trenton limestone of 
New York, and there is not the slightest doubt of its algal nature, 
although its relationship to recent forms is not altogether certain. 
Most students compare it to the modern Dasycladaceae, of the 
Green algae (Chlorophyceae ). 
The third restoration, Delesserites, was named by Sternberg, 
one of the early cultivators of paleobotany, from its resemblance to 
the existing Delesseria of Lamouroux, one of the Florideae or 
Brown algae, and, like the moc 
any 
ern genus, the Ordovician repre- 
sentative had a long ribbon-like thallus attached by a holdfast. 
The fourth restoration, Thammnocladus, is a Devonian non-cal- 
careous form of uncertain systematic position, which resembles the 
modern Rock weeds (Fucaceae or Dictyotaceae). 
The associated animals shown in the transparency include jelly 
fishes; eurvpterids and trilobites, which occupy the bionomic posi- 
tion of the crustacea of present day seas; primitive armored fishes ; 
and ancient sharks. 
rr 
— 
_ 
The oldest fossil algae do not appear to be appreciably different 
from those of modern seas, and we infer that it 1s a safe general- 
ization that those of the present are more diversified than those of 
the past, and portray for us all stages of algal morphology t 
may have existed in the vanished past. 
— 
lat 
