Wm. CarriUhers — PalcBohotany of Sweden. 23 



Nicholson and Etheridge had given a similar explanation of 

 Crossopodia, and other Nereites markings in their valuable con- 

 tribution to Silurian Paleontology (see their Monograph of the 

 Silurian Fossils of the Girvan district, pp. 304-318). 



Mr. Nathorst further experimented with fine mud obtained from 

 a depth of 12 to 15 ft., and which he placed, with all the animals 

 contained in it, in vessels of different depths. It was remarkable 

 how speedily after the vessels were at rest a great multitude of very 

 different tracks were produced. It became obvious that the sea- 

 bottom, where it consists of fine sediment inhabited by animals, 

 must be completely covered by trails of different kinds. The most 

 curious specimens procured were the trails of Goniada, Glycera, and 

 some other annelids which were found to be constantly branched as 

 in the impressions referred to the genus Chondrites. The impres- 

 sions, which are reproduced with minute fidelity and beauty in the 

 phototypes, were fixed by pouring liquid gypsum over the wet mud, 

 a method which Mr. Nathorst found to succeed in preserving the 

 most delicate markings. The trails of the annelid Goniada maculata, 

 Oersted, are very familiar as Paleozoic "Algse." In one of the 

 specimens of this creature's work (pi. ix. fig. 1), we find several 

 " plants " springing from one place, that in the centre is more 

 vigorous than the others, and gives off in an alternate manner from 

 its main axis a number of branches which are again branched. 

 This is so singularly faithful an outline of some fossil algae, that 

 nothing short of the testimony of so careful an observer as Mr. 

 Nathorst would convince one that it could have been produced by 

 an animal. The radiating tentacles of a Terehella produce a good 

 imitation of a plant. The impressions of an Amphiura, which had 

 been l^'ing on the mud with its arms extended, but had gently 

 moved the ends to and fro, gives a branching appearance, with a 

 flabellate outline to the " frond." The trails of molluscs like 

 Montacuta, and the larvae of some dipterous insects, obtained in a 

 garden after rain, are figured, showing long simple markings twisting 

 and turning on themselves, and giving very faithful representations 

 of the impressions referred to Palcsochorda. The markings made by 

 earth worms supply also very good materials for interpreting some 

 impressions generally treated as species of fossil algee. Mr. Nathorst's 

 figure on p. 19 may be compared with the figures of Physophycus 

 marginatus, Sch., on p. 87 of Saporta and Marion's recent work. 



Mr. Nathorst compares in detail, and with great care, the results 

 of his experiments with the list of Algce contained in Schimper- 

 Zittel's " Handbuch der Palaaontologie," and finds that all the im- 

 pressions brought together under the title " Alga incertce sedis " 

 can be produced by animals or by the mechanical action of plants 

 operated upon by running water. These Paleozoic alge are mere 

 impressions on the surface of ancient mud, and never exhibit any 

 remains of organic matter. It is very satisfactory to obtain such 

 clear evidence of their true nature, and to get rid of the false genera 

 and species which have unhappily burdened our handbooks, and of 

 the speculations which have been based on these misunderstood 

 markings. 



