440 BRITISH GRAPTOLITES. 



Compared with the size of the polypary, the thecae are relatively large, and 

 increase in size steadily from the proximal to the distal end of the polypary. 

 They are broad rather than long, and very closely set. 



Affiniti*'*. — Monog. discus is such a peculiar species in respect of its disc-like 

 habit and small size that it could hardly be confused with any other. Occasionally, 

 however, a specimen of M. turriculatus compressed from the apex of the conical 

 spire may present a somewhat similar disc-like appearance ; but in this case long 

 spines project in all directions from the disc or its component coils, and the 

 thecas are of a totally distinct type. 



Horizon and Localities. — Gala-Tarannon Beds (zone of M. crispus to zone of M. 

 vomeriiius var. crenulatus). 



S. Scotland : Rotten Clair, head of Walker Burn, Innerleithen; Old Quarry at 

 Cascade, 3^ miles ft.W. of Melrose ; Meigle Quarry, Galashiels ; Grieston. Ireland: 

 Portaferry. Wales: Bryn yr odin, near Llangollen; Tarannon River ; Afon Cwm 

 Caleb. ; Talerddig Railway ('utting; Gelli Stream, near Llanbrynmair ; Pen-y- 

 geulan, Wynnstay, etc. Lake District .• Rawthey Bridge, Sedbergli. 



Associates, etc. — Mono*/, discus is a fairly common fossil in the Gala-Tarannon 

 beds, though it does not seem to occur in the lowest beds of the series ; in the zone of 

 Monog. crispus it occurs with M. crispus, M. exiguus and M. Marri, it is also found 

 with M. griestoniensis at a higher horizon, and more sparingly with ill. vomerinus var. 

 crenulatus and .1/. priodon at the top of the Gala-Tarannon Series. 



Collections. — Geological Survey of Scotland, Belfast Natural History Museum, 

 L. J. Wills, Lapworth, and the Authors. 



Monograptus tortilis, Linnarsson. Plate X LI V, fig. »'». 



1881. Monograptus tortilis, Linnai-sson, Geo!. Fiiren. i Stockholm Foihandl., no. 68, vol. v. no. 12, 

 p. 514, pi. xxii, figs. 19, '20. 



Polypary 3 — 4 cm. in length, arcuate (? spiral), incurved, fairly robust, widening 



from its initial region to a maximum breadth of 1*5 mm. or more. Thecae 



nine to ten in 10 mm., of the general type of those of M. Marri, but with the 



isolate apertural region less recurved, and with rather less than one-half of 



the theca involved in the hook, which occupies about two-thirds of the 



breadth of the polypary. Overlap one-half to one-third of total length. 



Description. — The polypary exhibits strong curvature, with the thecae on the 



concave edge; it frequently has a curiously bent appearance, as if it were broken 



or had grown sub-spirally ; in the specimens known it is seen to widen slightly 



throughout its length. 



The thecae are of the general type of those of .1/. Marri with a similarly distinct 



