PROCEEDINGS OF SECTION C. 377 



2._0N THE RELATIONSHIP OF THE GENUS GIRVANELLA, 

 AND ITS OCCURRENCE IN THE SILURIAN LIME- 

 STONES OF VICTORIA. 



% FREDERICK CHAPMAN, A.LS., F.R.M.8., National Museum, 



Melbourne. 



[With Three Plates.] 



INTRODUCTION AND DESCRIPTION OF THE GENUS. 



The genus Girvanella was established by the late Professor H. A. 

 Nicholson and Mr. R. Etheridge, jun., in 1880, to include certain 

 minute tubular organisms, which had also been noticed by Dr. H. B. 

 Brady, occurring with some frequency in the Craighead limestone 

 (Ordovician) of Girvan, Ayrshire. Similar nodule-forming organisms 

 have since been met with in limestones of various ages, ranging from 

 the Cambrian to the Jurassic ; and others, no doubt allied to fossil 

 forms, exist at the present day. As a rock-forming agent Girvanella 

 has played a very important part in Palaeozoic and Mesozoic times, and 

 it has been shown in detail by Wethered and other investigators that 

 many of the oolitic rocks of Jurassic and Carboniferous ages partly 

 owe their origin to this microscopic fossil. 



The question of the nature of this tubular organism, whether 

 a form of animal or plant life, has not yet been satisfactorily answered, 

 but the general consensus of opinion is in favor of the latter view. 

 Some authors believed it to be of animal origin, and one of the fora- 

 minifera, or even a sponge, although there seems to be no evidence 

 to support the latter view, whilst others equally held it to be a form 

 of the calcareous algae. Any fresh evidence, therefore, bearing on this 

 question, which may help to settle the relationship of Girvanella, is of 

 scientific value, and in view of this the following notes have been 

 written. 



The original description of the genus Girvanella is as follows (a) : — 

 "Microscopic tubuli, with arenaceous or calcareous (?) walls, 

 flexuous or contorted, circular in section, forming loosely compacted 

 masses. The tubes, apparently simple cylinders, without perforations 

 in their sides, and destitute of internal partitions or other structures 

 of a similar kind." 



The first-described species was thus defined (6)—-" Girvanella 

 frohlematica, Nich. and Eth., jun., sp. nov. Spec. Char. — Tubes from 

 l-600th to l-700th of an inch in diameter, not observed to taper, 

 twisted together in loosely reticulate or vermiculate aggregations of a 

 rounded or irregular shape, which seem to be mostly from l-20th to 

 1-lOth of an inch across." 



OUTLINE OF RECORDED OCCURRENCES. 

 After the discovery of Girvanella in the Upper Ordovician Hme- 

 stone of Scotland by Nicholson and Etheridge, jun., Mr. S. A. Miller, 



(«) Nicliolson and Etheridge, jun. ('80), p. 23. 

 (6) Nich. and Eth. ('80), p. 23, pi. ix., fig. 24. 



