FOSSIL MEDUS &. 
By CuHarues D. Waucort. 
INTRODUCTION. 
The occurrence of impressions of medusz on the Jurassic lithographic 
limestones of Solenhofen has long been known and is referred to in nearly 
all comprehensive works on paleontology. In 1881 Dr. Nathorst called 
attention to certain problematic fossils from the Lower Cambrian rocks of 
Sweden, which he regarded as casts of the impressions of the lower side 
of medusze that had been left on the soft mud by the tide or had been 
thrown up by the waves; others were thought to be casts of the gastric 
cavity of a medusa having a large mouth opening and a large gastric 
cavity. In 1891 I called attention to the Lower Cambrian Dactyloidites 
asteroides, suggesting that it might be the impression of the mouth and gastric 
cavity of a medusa. In the last four years I have studied, during short 
intervals of time taken from administrative work, large collections of 
medusze from the Middle Cambrian rocks of the Coosa Valley, Alabama. 
The original plan was to incorporate the results in a monograph on the 
Middle Cambrian fauna; but now that the study has included the Lower 
Cambrian and Jurassic types, it seems advisable to publish a separate 
memoir on the subject of fossil medusze, in order to place before students a 
full review of the subject. 
The Middle Cambrian medusz will first be deseribed, and then, in 
order, the Lower Cambrian of the United States and of Sweden and 
Bohemia, and the Jurassic of Bavaria. 
MON Xxx——1 1 
