48 FOSSIL MEDUS.E. 



medusa on account of its pentameral symmetry. Replying to this, Dr. 

 Nathorst stated that he had studied the recent forms, Aurelia aurita and 

 Cyanea capiUata, in large numbers, and found in the latter five-sided as 

 well as four-sided symmetry. It is more rare in A. aurita, though both 

 three-sided and five-sided symmetries exist, in addition to the usual tetra- 

 meral symmetry. 1 



From the evidence adduced by Dr. Nathorst, and from a comparative 

 study of both the fossil and the recent forms, I am led to regard the Swedish 

 Lower Cambrian fossils as evidences of the presence of medusa? in the 

 Lower Cambrian seas of Sweden. 



It may be doubtful whether Dr. Nathorst's interpretation of Eophyton, 

 as made up of trails produced on mud by medusa?, is correct, but it is quite 

 probable that in some instances they have originated as he suggests. As 

 regards others, however, I think there is little doubt that they owe their 

 origin to the trailing of algae over the bottom. On this account I have 

 inserted a description (pp. 59-65), rather freely illustrated, of the fossil 

 forms that have been referred to Eophyton. 



In an article on "Illustrations of the fauna of the St. John group, 

 No. V," Mr. Gr. F. Matthew quotes the descriptions of Medusina princeps, 

 M. radiata, and M. costata from Linnarsson. He also describes five forms 

 of what he considers to be trails or the imprints of tentacles of medusa?, 

 under the generic name of Mcdusichnites. 2 



Through the courtesy of Mr. Matthew, I have examined the original 

 specimens, and I find that, with possibly the exception of fig. 1 of his PI. 

 XIII, all of the varieties of Medusichnites might much better be referred to 

 markings of inorganic origin. I have seen large areas of Lower Cambrian 

 shales in Rensselaer County, New York, covered with markings like those 

 shown by his fig. 4 of PI. XII and fig. 1 of PI. XIII. These were studied 

 in connection with the investigation of medusa-like trails, and the conclu- 

 sion reached was that they could not have had such an origin. 



In order that the student may have the means of comparison, I have 

 introduced photographs of some of the typical specimens described by Mr. 

 Matthew. (See PI. XLVI.) 



1 Loc. cit., p. 177. 



2 Trans. Eoyal Soc. Canada, Vol. VIII, 1890, sec. 4, pp. 143-146, Pis. XII, XIII, fig. 1. 



