84 GIBTANJSLLA. 



Genus GIRVANELLA, Nicholson & Etteridge. 

 [Silurian Foss., Girvan District, p. 23, 1880.] 



Girvanella pisolitica, Wethered. 



[Geol. Mag. (iii.), vol. ri. p. 200, pi. vi. figs. 8, 10, 11, 1889.] 



1889. Gii-vanella pisolitica, TVethered, Geol. Mag. [iii.], vol. vi. p. 200, 



pi. vi. figs. 8, 10, 11. 

 1891. G. pisolitica, Eothpletz, Zeitschi-. deutsch. geol. Ges. vol. xliii. p. 295. 



Mr. Wethered describes tlie species as follows : — " This species 

 occurs in the form of flattened spherules varying in size from 

 1 to T^ inch in greatest diameter. In the centre of each spherule 

 there is a nucleus which is surrounded by calcareous tubuli with 

 weU-defined walls, and averaging about s^o of an inch in diameter, 

 though some are smaller. In some instances, more especially in 

 the larger spherules, the tubes bend and twist about in a truly 

 vermiform manner, often assuming the form of a flattened coil 

 . . . . The tubes are also branching, and are larger than those 

 of G. prohlematiea." 



P. 4481. Two sections of oolitic grains containing G. pisolitica 

 from Cleeve HiU, Grloucestershire (Inferior Oolite). 



Presented ly E. Wetliered, Esq., 1892. 



The wide geological range of Girvanella, from Cambrian rocks 

 upwards, and the very small knowledge we possess as to the nature 

 of the genus, render it inadvisable to attempt a specific diagnosis 

 and terminology for the numerous forms of tubules met with in 

 Oolitic rocks. Eothpletz ' and Brown ^ have expressed the opinion 

 that Girvanella is probably a calcareous alga of the group Siphonese. 

 I have elsewhere suggested that the tubules may be the sheaths of 

 Cyanophycese, but we require more information before we can hope 

 to speak with confidence as to the systematic position of the genus.' 



In addition to the type named by Mr. Wethered Girvanella 

 pisolitica, other species have been described by the same author 

 from Jurassic Oolites, but none of these are represented in the 

 Museum collection. 



1 Eotlipletz (91), p. 301. 

 ' Brown (94), p. 203. 

 3 Seward (98), p. 125. 



