48 THALLOPHYTES, BRYINAE. 



which corresponded more or less perfectly with certain supposed Alga- 

 types. In some cases the result was striking. Eophyton, Torell was 

 produced with the greatest ease by passing bits of Algae and parts of 

 animals over soft mud. The casts of tracks of a crab, Corophium longicorne, 

 gave a figure which answers so exactly to the Silurian and Carboniferous 

 genus Crossochorda and also to Gyrochorda from the Tertiary strata of the 

 Jura, that Saporta l himself has consented to remove these genera from the 

 Algae. Precisely similar tracks, according to Etheridge and Nicholson, are 

 also made by Purpura lapillus 2 . Williamson 3 again took casts in the same 

 way of the furrows left behind by the retreating tide on the shore of the 

 sandy coast of Llanfairfechan in N. Wales, and obtained figures which 

 look exactly like the forms of leaves of recent Florideae, such as 

 Wormskioldia sanguinea. This is quite enough to show how little value is 

 to be set upon the Halymenitae, Delesseritae, Laminaritae, and Caulerpitae 

 of authors, even if there can be no doubt that some of them are real im- 

 pressions of Algae ; this is proved, for example, in the case of Halymenites 

 Arnaudi 4 by the presence of a Membranipora, which has been preserved at 

 one spot in the impression. 



Saporta, like Schimper before him, lays special weight on the copious 

 branching shown by many of the algal remains which he defends. He 

 denies with Schimper that there can be any branched animal tracks. 

 Zeiller 5 however very recently made known an excellent instance of this 

 very thing. He observed in Normandy on the moist clay bottom of some 

 dried-up puddles some curious branched rounded elevations formed simply 

 of small raised lumps of clay, and agreeing very nearly in outward appear- 

 ance with the Jurassic genus Phymatoderma ; these lumps formed the roof 

 of a system of passages which had been made by some burrowing animal 

 beneath the surface of the ground. The impressions of the claws on the 

 inner wall of the passages were evidently those of the common mole-cricket, 

 which with its rounded back had lifted up the thin roof of soil and broken 

 it up into small pieces. In a similar manner various forms may be explained 

 in which the theory of foot-tracks has difficulties to encounter, and this may 

 be the case especially with many of the branched forms of Bythotrephis and 

 Chondrites. The variety of the tubes formed by worms and other creatures 

 on the bed of the sea must certainly astonish every one who by frequent 

 visits has made a close acquaintance with the strand at low water. 



Hall 6 has described a specimen as an Alga under the name of Dictyo- 

 lithes Beckii from the Medina sandstone of the Upper- Silurian formation of 

 the State of New York. This is at once recognised to be the cast of a clay 

 floor in a half-dried state and with the cracks forming polygonal areolas as 



1 de Saporta (1), p. n. a Nathorst (1). 3 Williamson (2). 4 de Saporta (1), t. 2. 



s Zeiller (1). e Hall (1), vol. ii, t. 2, f. i. 



