MIDDLE CAMBRIAN. 3 
Jurassic, and still earlier, in the Middle and probably in the Lower Cam- 
brian. The conclusion is that the acraspedote meduse were mainly differ- 
entiated in early Cambrian if not in pre-Cambrian time. It is evident that 
we yet have much to learn of the medusiform ancestors of the Hydrozoa. 
FOSSIL MEDUSA OF THE MIDDLE CAMBRIAN TERRANE. 
As related in the Preface, a collection of fossils from the Coosa Valley, 
Alabama, made in the summer of 1886, contained a number of semicherty 
nodules, some of which had fragments of trilobites and brachiopods of the 
Middle Cambrian fauna attached to and buried in them; others had a radi- 
ate-lobed appearance that suggested the sea-urchin, while a few of the flat 
nodules had a fossil spread out on them that resembled a star-fish.. Large 
collections were made during the succeeding years, but it was not until 
1893 that I felt assured that the so-called ‘“star-cobbles” were fossil medusze. 
There are now more than 9,000 specimens in the collections of the United 
States Geological Survey. These afford ample material for the study of 
two types’ that may be referred to the Discomedusz. 
MODE OF OCCURRENCE. 
The shale containing the fossils breaks down into clay on exposure to 
moisture, heat, and cold, and the siliceous nodules weather out from it and 
are found in large numbers on the surface and along the drainage channels. 
Fragments of trilobites, etc., occur in the shale, and are attached to and 
embedded in many of the nodules, and, more rarely, attached to specimens 
of the medusze. The fossils common to the shale and nodules are: 
Laotira cambria Walcott. Hyolithes. 
Acrotreta. Ptychoparia antiquata Salter. 
Lingulella. Ptychoparia. 3 sp. (2) 
Scenella. Olenoides curticei Walcott. 
Stenotheca. 
Of the nodules, about one-quarter show more or less of fossil medusz. 
A few of the larger flat nodules have several medusz attached to each, but 
usually a single individual forms the entire nodule, or serves as the nucleus 
for a nodule that may vary in form and size from all its fellows. It is rare 
to find two that agree in all respects. 
1A notice of these appeared in the Proceedings of the United States National Museum, Vol. 
XVIII, 1896, pp. 611-614. 
