220 THE PEOCEEDINGS OF THE LINNEAN SOCIETY 



extremity than the remainder. These ribs have the appearance 

 of plaits folded from the outside towards the centre. The inner 

 margin of each fold near the axis presents a well defined sharp 

 edge, which becomes slight and almost insensible at the margin. 



The surface is covered with three distinct series of folds ; 

 these divide the surface into three areas, in each of which one 

 series appears more distinct than the others. The first area, 

 counting from the external edge, extends to about 3 millemetres 

 from the margin ; the second zone has a width of about 4 mille- 

 metres ; the third occupies the remainder of the surface. 



In the last area the ribs are crossed by twelve or thirteen folds, 

 at right angles to the direction of the ribs only in the centre rib. 

 These have the appearance of being folded from the anterior 

 outline. The next consists of four regularly curved concentric 

 folds, appeariDg to be folded from the exterior towards the centre. 

 In the external area the folds are less regular and form parts of 

 curves of larger radii than the preceding. These appear also 

 as if folded inward. These different series are not however 

 confined to the areas specified, but extend to the other parts, 

 though they are not then so distinct. 



This species is certainly very distinct from the characteristic 

 Devonian species, Bronteus flabellifer, though, from its fan-like 

 pygydium, it well deserves the name. It appears to be more 

 related if not identical with Bronteus Partschi, the pygydium of 

 which is described by Professor Koninck. * Except in the 

 actual size, the description of Professor Koninck, as far as it 

 goes, applies well enough to the smaller specimens I have 

 obtained. According to the same author, M. Barraude found in 

 Bohemia Bronteus Partschi in the lower part of the Upper 

 Silurian. 



The specimen of Broriteios I have figured (figs. 4, 5, 6, and 8), 

 are most abundant about the middle of the Hume beds, some few, 

 however, I have obtained lower, and two specimens in the Yass 

 beds. 



In the specimens of different sized individuals, there is con- 

 siderable variation in the proportions of the corresponding parts. 



* Page 57. 



