58 The American Geologist. January, i899 
The American species are all Cambrian and belong to four genera, 
Brooksella Laotira, Dactyloidites and Medusina. The two former 
are now described for the first time, and have been obtained from 
silicious nodules of the Coosa valley, Alabama, first observed and 
collected by Dr. Cooper Curtice. The Medusse occur plastered upon 
and imbedded in the silicious nodules (called ''star cobbles") which 
have been contained in a yielding shale. 
The first twenty pages of the memoir are devoted to a description 
of the mode of occurrence of these interesting fossils, and of the litho- 
1( gical and chemical peculiarities of the nodules which are the medium 
of their preservation. The question of their relation to the sponges 
is also discussed. 
Of the two genera described from this locality Brooksella is the 
more simple form. This genus is referred by the author with doubt 
to the suborder Rhizostomae of the Discomedusae and Cannorhiza con- 
nexa is considered the nearest living form. Mr. Walcott illustrates 
this by a restoration of Brooksella alternata and a section of the 
species above named; the structural relation is quite marked, and all 
the essential part of a Discomedusan appear to have been recognized, 
except the reproductive organs. 
Laotira is a more complex structure. Some examples are simple, 
like Brooksella, others are compound structures supposed to be pro- 
duced by fission, as in some living Medusae. In the compound forms 
the regular radial symmetry is more or less obscured, and a bilateral 
symmetry prevails. Diagrammatic representations are given of three 
conditions of Laotira, from the simple to the most complex. No re- 
productive organs have been observed in Laotira, in which the in- 
crease of individuals is supposed (as above observed) to be due, in 
part at least, to fission. All the varieties observed are referred to one 
species, Laotira cambria. 
The above species of fossil Medusae were found in the Middle 
Cambrian rocks of Alabama, but a form which is now referred to the 
Discomedusae by Mr. Walcott was found some years ago in slates, 
referred to the Lower Cambrian, in Middle Grenville, New York. 
This was taken by the discoverer. Dr. Asa Fitch, to be a seaweed, 
and described as Bothotrep/iis ? asteroides. Subsequently it was more 
fully described by Prof. Jas. Hall under the generic name of Dacty- 
loidites. He thought it referable to sponges or possibly to marine 
algae. 
Unfortunately all the examples of this fossil are completely flat- 
tened out, and consist of scarcely more than a faint dark stain on the 
layers of the slate. Mr. Walcott has found a few raised somewhat 
in relief, and by comparison with the Middle Cambrian forms of the 
Coosa valley has been able to satisfy himself that the impressions are 
those of a species of the Discomedusae. A similar form has been 
fi'und at Parker's quarry, Georgia, Vt. 
About twelve pages of Mr. Walcott's memoir are taken up with a 
description of the Lower Cambrian Medusas of Sweden and Bohemia, 
