DICRANOGRAPTUS. 



173 



108 d and 



Nichols, 



— Dicranograptus 

 Hopk. 



d. Uiiiserial stipo in full relief, showing 



one aspect of thecae. On same slab 

 as fig. 108 c. 



e. Thecse in another aspect. Enlarge- 



ment of part of PL XXV, fig. 1 c. 



8. Scotland: Dobb's Linn 

 horn Burn ; Glenkiln Burn 



mesial spines fully 1 mm. in length, and in some cases these spines may assume 

 abnormal proportions (fig. 109/). There is a marked change in the direction 



of growth of the thecae where the uniserial stipes 

 diverge, the thecae growing chiefly outward and 

 but very slightly upward in their apertural regions. 

 This change, combined with their increase in length, 

 gives the appearance pointed out by Hopkiuson of the 

 stipes " being joined beyond the point of bifur- 

 cation." In specimens preserved in relief this effect 

 disappears. 



Affinities. — D. NicJwlsoni perhaps approximates 

 most closely to Dicranog. rectus in general form, but 

 it differs in the shape of the thecae and in the 

 uniform width of the uniserial stipes. From other 

 species its form is sufficient to distinguish it. 



Horizon and Localities. — Grlenkiln Shales and 

 Lower Hartfell Shales. 



Hartfell; Berrybush Burn; Gairy, head of Garry- 

 Birnock Burn, head of Wandel Water ; Craiginichan 

 Scaurs ; Morroch Bay ; Cardockan Burn, Loch Dee, 

 etc. N. Wales : Tiddyndicwm. 8. Wales: Southhill 

 Ford ; between Peblewin and Stoneyford Railway, 

 Pendwr. Ireland : Bally grot. 



Associates, etc. — D. NicJwlsoni is a very abundant 

 fossil at certain horizons in S. Scotland, especially 

 towards the top of the Glenkiln Shales, where it 

 occurs with Dicellog. sextans, Glossog. HiiwJcsi, and 

 other forms ; and in the lowest beds of the suc- 

 ceeding Hartfell Shales, where it is associated with 

 Climacog. ScJiarenbergi, Climacog. bicornis, Climacog. 

 Wilson I, and other Dvplograpti. It is exceedingly 

 abundant and beautifully preserved in the exposure 

 of the zone of Climacog. Wilsoni in the main cliff 

 at Dobb's Linn, and from this locality the best 

 specimens known to us were obtained. There are 

 good examples in the collections of the Geological Survey of Scotland, the 

 Sedgwick Museum, the British Museum of Natural History, and in the private 

 collections of Lapworth and the Authors. 



/. Biscrial portion of a flattened speci- 

 men, showing abnormal spines and 

 appearance of web in axil. En- 

 largement of part of PI. XXV, 

 fig. 1 e. 



g. Thecae of uniserial stipes. On same 

 slab as PI. XXV, «-»■. 1 c. 



