444 Prof. Garwood — Calcareous Algce. 



Thus the recent detection in the lowest Cambrian rocks of the 

 Antarctic Continent of a form which appears to be referable to this 

 genus enables us to trace the ancestry of Solenopora back almost to 

 the earliest rocks in which fossils have yet been discovered, while 

 the gap in the succession which previously existed between the 

 Ordovician and Jurassic forms was decreased by the description in 

 1908 by Professor Rothpletz of a new species Solenopora gotlandica, 

 from the Silurian rocks of Faroe Islands in Gotland.' A large 

 number of deposits, however, still remained, between the Gotlandian 

 and Lower Jurassic beds, from which no example of Solenopora had 

 so far been recorded. 



The identification, therefore, a few years ago, by Dr. G. J. Hinde, 

 of examples of this genus from among the nodules I had collected 

 from the Shap dolomites, is of considerable interest, as the presence 

 of Solenopora in the Lower Carboniferous rocks of this country 

 materially decreases the gap in our knowledge of the succession of 

 forms belonging to this genus which had previously existed. 



Girvanella. 



This organism, which is now known to be widely distributed in 

 the Palaeozoic and Mesozoic rocks of this country, was originally 

 described in 1878 by Nicholson and Etheridge, jun., from the 

 Ordovician rocks of the Girvan district. The genus was established 

 to include certain small nodular structures composed of a felted mass 

 of interlacing tubes, having a width of 10 and 18 /i, the cells being 

 tj'pically simple, imperforate tubes without visible internal partitions. 

 The geno-type, G. problematica, was, however, at that time referred 

 to the Rhizopods and regarded as related to the arenaceous fora- 

 minifera.^ In 1888 Nicholson, in redescribing this genus in the 

 Geological Magazine, compares Girvanella with the recent form 

 Syring ammina fragillissima of Brady. 



More recently Mr. Wethered has shown that an intimate association 

 frequently exists between Girvanella tubes and oolitic structure, and 

 he has described several new species of Girvatiella from the Palaeozoic 

 rocks and also from certain Jurassic limestones. 



The reference of Girvanella to the Calcareous Algae, though not yet 

 supported by incontestable evidence, has been advocated by several 

 writers in recent years. Even as long ago as 1887, Bornemann, in 

 describing examples of Siphonema {Girvanella, Nich.) which he had 

 discovered in the Cambrian rocks of the Island of Sardinia, suggested 

 that this organism might belong to the Calcareous Algae. 



In 1891 Rothpletz ^ noticed that some of the specimens of Girvanella 

 which he had examined were characterized by dichotomous branching 

 of the tubes ; on this account he removed the genus from the Rhizopods 

 to the Calcareous Algae, placing it provisionally among the Codiaceae. 

 Three years later Dr. A. Brown, in summing up the evidence in 

 favour of the inclusion of Solenopora among the Nullipores, expressed 



' Kungl. Svenska, Vets. akad. Handl., Bd. 43, No. 5, pi. iv, pp. 1-5 and 

 14, 1908. 



^ Silurian Fossils in the Girvan District, 1878, p. 23. 

 ^ Zeitschr. d. D. Geol. Gesell., 1891. 



