CLIMACOGRAPTUS. 



213 



Ireland : 



8. Scotland: Dobb's Linn; Long Linn, Lockerbie; Thirlstane Burn 

 Donaghadee. 



Associates, etc. — CI. innotatus is a fairly abundant fossil in the Birkhill Shales 

 of S. Scotland and Ireland. It occurs associated with Cephalog. acuminatus, 

 Dlplog. vesiculosus, Climacog. scalaris var. normalis, CI. rectangvlaris, Monog. I run is, 

 and Monog. gregarius. 



Collections. — Sedgwick Museum, British Museum (Natural History), Lap worth, 

 and the Authors. 



Group V. 



Climacograpti in which the free edge of the theca is slightly inclined, and the 

 apertural margins are thickened and produced into spines. 



Climacograptus tuberculatum, Nicholson. Plate XXVI, figs. 7 



isr>«>. 



Climacograptus tuberculatum, Nicholson, Ann. Mag. Nat. Hist., ser. 4, vol. iv, p. 2c 



Polypary 1 — 2 cm. in length, widening fairly rapidly to a maximum breadth 

 of 2 mm., which is then maintained up to the distal extremity; proximal 

 end adorned with two short, stout, curved or horizontal spines. Sicula 

 unknown. Thecas twelve to ten in 10 mm., alternate, free edges straight 

 or with slight concave curvature, overlap small ; apertural margins situated 

 in shallow elliptical depressions occupying one-fourth to one-third the 

 width of the polypary, and having their lateral angles adorned with a 

 linear series of tubercles. 

 Description. — All known specimens of CI. tuberculatus are poorly preserved. 

 The polypary attains its maximum width fairly 

 quickly ; proximally it is only OS mm. wide, but this 

 dimension is doubled within the first millimetre of 

 length, and the same rate of increase is maintained. 

 The spines at the base are shorter and stouter in 

 proportion than those of CI. bicornis, and they are 

 commonly directed horizontally at first, though 

 subsequently they may be slightly curved and 

 directed somewhat obliquely downward. The vir- 

 gella is conspicuous but small. The so-called tubercles 

 on the lateral edges of the apertures are best seen 



Fia. 144(7.— Climacogra.pt 

 Nich. 



Proximal end, showing thickening of 

 apertural margins and spines. 

 Dobb's Linn, Lower Birkhill Shales. 

 Coll. British Museum (Nat. Hist.). 



