14 SCIENCE PROGRESS. 



of growth. In another species from the same rocks, 

 G. incrustans, 1 the narrow tubules form a crust round a 

 calcite nucleus. The Jurassic Oolites have afforded such 

 species as G. pisolitica, G. intermedia and G. minuta. In 

 all these cases the organism consists of tortuous and 

 aggregated tubules exhibiting certain variations in size and 

 manner of arrangement. The frequent association of this 

 structure with oolitic grains leads Wethered to the conclu- 

 sion that the spherules of such rocks must be referred rather 

 to an organic than to a concretionary origin. 



Dr. Hinde has called attention to the occurrence of 

 Girvanella in Ordovician rocks in the province of Quebec, 

 and to the discovery by Bornemann of similar structures 

 in Cambrian rocks of Sardinia. 2 Bornemann has instituted 

 a new genus Siphonema 3 for certain incrusting calcareous 

 algae consisting of minute tubular cells. He compares the 

 Sardinian genus to the recent Scytonomacece, and expresses 

 the opinion that in all probability many of the oolites from 

 various geological horizons will be found to supply similar 

 proof of their organic origin. The nature of these Sar- 

 dinian fossils and their concentric disposition round frag- 

 ments of shells, crinoids or corals are very like that of 

 Girvanella, and there can be little doubt that Bornemann's 

 genus is the same as that previously established by Nichol- 

 son and Etheridofe. 



The species of Siphonema, S. incrustans, which occurs 

 in the Sardinian rocks has also been found by Bornemann 

 in a limestone boulder which probably came from Baltic 

 rocks of Silurian age. Additional information has been 

 collected by Wethered as the result of his microscopical 

 researches on the structure of Oolitic rocks from the Cottes- 

 wold Hills. 4 In a still more recent communication to the 

 Geological Society the same author refers to the occurrence 

 of Girvanella tubules in Devonian limestones from South 

 Devon ; 5 and on another occasion the existence of G pro- 



1 Wethered (2), p. 280, pi. xi., figs. 1 a, b. 



2 Wethered (2), p. 282. s Bornemann (1), pi. ii. 

 4 Wethered (3). 5 Wethered (4). 



