A. G. Nathord — Markings on Camhrian Rocks. 25 



and thus attributed to Sponges, Corals, Crinoids and Echinoderms ! 

 These fossils retain no organic structures, and only the form has 

 been preserved. As regards those described as corals and sponges, 

 such authorities as Lindstrom and Eoemer repudiate their connexion 

 with these groups. 



It appears that Herr Nathorst was led to compare these fossils 

 to the impressions of Medusas by casually observing the similarity 

 of form between some specimens of _ the existing Medusa, Aurelia 

 aiirita, thrown up on the beach at Oresund, and specimens of so- 

 called Spatangopsis from the Eophyton sandstone at Lugnas, which 

 are in the Stockholm Museum. This similarity induced him to 

 try the experiment of obtaining casts of these existing Medusae by 

 means of dilute plaster, and the resemblances between the artificial 

 and the natural impressions were so close that the author regards it 

 as proved that the fossil impressions result from Medusaj. The impres- 

 sions most commonly met with, have the shape of a central, elevated 

 pyramidal body, from which radiate four or five arms or rays. 

 This form has resulted from the settling down of the Medusa into 

 the mud, which, by the infilling of the gastral cavity, has pro- 

 duced the pyramidal body, whilst the radiating impressions are 

 those of the prolonged angles of the mouth. Another form which 

 generally occurs free is believed by Nathorst to result from the in- 

 filling of the gastral cavity of those animals which have died or been 

 thrown on the strand with the mouth uppermost. 



The author treats at length the various points of comparison 

 between the fossils and existing Medusae of various families, and 

 refers the forms to three species : — Medusites radiatus, Linnars. sp. 

 =Astylospo7igia radiata, pp. Linnars.; M. favosus, ii.s'p=iProtolyellia 

 princeps, Torell, and Astylospongia radiata, pp. Linnars. ; and M. 

 Lindstromi, Linnars. s-p.=^ Spatangopsis costata, Torell, and Agela- 

 crinus ? Lindstromi, Linnars. In addition to these forms, which are 

 regarded as resulting from the impressions and infillings of the 

 central portions of Medusae, the author attributes the peculiar 

 spiral casts in the same rocks, named by Torell Spiroscolex spiralis, 

 to the tentacles of Medusae. 



In a supplement the author thinks that the life-habits of the 

 existing genus Polyclonia, recently described by Profs. Moseley 

 and Agassiz, tend to show further the probability of the Medusa- 

 origin of these fossils. Folyclonia lives in great numbers near 

 the muddy bottom of certain seas, and its movements would tend 

 to produce the Eophyton markings, whilst it has also the habit of 

 turning its bell uppermost, and this, in the dead specimens, would 

 facilitate the entrance of sediment into the gastric cavity. 



The facts brought forward in this paper indicate at least great 

 probability that the author's conclusions are correct, and he may 

 be congratulated on having carried our knowledge of the existence 

 of these organisms back from Jurassic to Cambrian times. 



G. J. H. 



