1 60 



BRITISH GRAPTOLITES. 



exclusive of the apertural spine ; it is often clearly seen in the axil of well 

 preserved specimens. Its apex, however, is frequently broken off, and it then 

 Figs, ioo a and b.—Diceiiograptuseiegans, appears as a mere node between the stipes and 



hence has often escaped detection. Its apertural 

 spine and the lateral spines of th. 1' and th. I 2 are 

 \a\ /J-v always conspicuous, and are sometimes as much 



as 2 mm. in length. Occasionally traces of a 

 membranous film are visible within the axil extend- 

 ing for a short distance up the stipes, never, how- 

 ever, to a sufficient extent to conceal the apex of 

 the sicula. The proximal thecae grow horizontally 

 for the greater part of their length, giving off a 

 spine where a change to the upward direction takes 

 place ; they are narrower than those developed later. 

 Th. 2 1 and th. 2 2 grow also for a considerable 

 portion of their length in a horizontal direction, and 

 hence the square form of the axil is acquired. 



The thecae overlap for about one third of their 

 length, which averages 1*5 — 2 mm.; the free outer 

 wall generally shows marked sigmoid curvature, but 

 in certain states of preservation is straighter, though 

 never parallel to the axis of the stipe. The pouch-shaped excavation into which 

 the introverted aperture opens is wide and occupies half the breadth of the stipe. 



Affinities. — The general form of the polypary of 

 D. elegans is characteristic and serves to distinguish 

 it from all other Bicellograpti. 



Horizon and Localities. — Lower Hartfell Shales 

 (zone of Pleurog. linearis). 



S. Scotland : Dobb's Linn ; Hartfell Spa ; Craig- 

 michan Scaurs, etc. Ireland: Carnalea ; Craigavad; 

 Coalpit Bay, etc. 



Associates, etc. — D. elegans is an abundant species 



in the zone of Pleurog. linearis, where it occurs 



associated with the zone fossil, Leptog. flaccidm, 



Diplog. truncatus, Dialog, foliaceus (auct.), Glimacog. tubuliferus, Dicellog. Morrisi, 



Dicellog. pumilus, etc. There are good specimens in the collections of the Natural 



History Museum, Sedgwick Museum, and Lapworth. 



Proximal end, with " film." On same 

 slab as PI. XXIII, fig. 2 d. 



Proximal end with abnormally de- 

 veloped lateral spines. Hartfell 

 Spa. Hartfell Shales. Coll. Lap- 

 worth. 



Figs. 100c and d. — Dicellog raptus elegans, 

 Carr. 



r. Proximal thecse, showing marked 

 introtorsion. Part of same speci- 

 men as Fig. 100 a. 



d. Distal thecre, not true profile view, 

 and thus showing less introtorsion. 

 On same slab as Fig. 100 b. 



