LOWER CAMBRIAN. 53 



In a letter received from Dr. Nathorst, dated February 19, 1892, he 

 says that "as to Medusites lindstromi, it has now been proved with certainty 

 that it is a true medusa, a specimen having been found showing the 

 impression of the genital hollows." A pencil sketch accompanied the 

 note. More recently a sketch of the specimen was published, 1 and I have 

 had a copy made, as shown by fig. 1 of PI. XXX. The mouth is at M, the 

 genital hollows at Gr, G, G, G, and the radiating imprints between the 

 latter and the outer margin. 



Among some specimens of this species received from the Geological 

 Survey of Sweden, I find one that shows very clearly the casts of four 

 hollows in the roof of the gastric cavity; also, as rounded protuberances 

 between the four raised angles, the genital sacs, g, //, g, g, of PI. XXVIII, 

 figs. 3a, 3b. The roof hollows are shown in a five-lobed specimen by 

 Dr. Linnarsson (loc. cit., fig. 9 of PI. I). The casts of the genital sacs 

 were noted by Messrs. Torell and Linnarsson, and Dr. Nathorst describes 

 them in detail. He compares casts that he had made of the lower sur- 

 face of An reiki aurita with the casts from the Lower Cambrian at Lugnas, 

 and his illustrations show a remarkable resemblance between them. On 

 Pis. XXX and XXXI, I have reproduced photographs of casts in soft 

 plaster which I made of the lower surface of Aurelia flavidula, in order to 

 furnish the student with the means for a direct comparison of the casts of 

 the recent and fossil forms. The cast of the lower side of Aurelia (figs. 2 

 and 3 of" PI. XXX) shows the quadripartite pyramid formed by the cast of 

 the mouth opening; also the outline of the genital sacs. This may be 

 compared with the cast of Medusina costata, fig. 1 of PI. XXX. The cast 

 of the uncompressed genital sacs of the fossil medusa is shown by g, g, g, g, 

 of tigs. 3a, 3b of PI. XXVIII. 



Dr. F. Schmidt describes the occurrence of a specimen of this species 

 in Ksthonia, one of the Baltic provinces of Russia, as follows: 



Up to the present only a single specimen of this form is on hand, which agrees 

 perfectly with the specimens from the Eophyton sandstone of Sweden. The specimen 

 is five-rayed, and rises into a regular five-sided pyramid with raised, obtuse ribs. 

 The lower side is arched, with a flat depression in the middle. It shows most 

 agreemeut with Liuuarsson's F. 8. 



The height of the specimen is 40""", the largest horizontal diameter 53""". 



■Sveriges geolngi, af A. G. Nathorst, Stockholm. (No date.) Received by Library of U. S. 

 Geological Survey in 1895. 



