482 



BRITISH GRAPTOLITES. 





fig. 337.— Monogmptus communis, var. especially in the proximal region, measuring full v 



rostratus, no v. l ,j 1 o o ■/ 



1*8 mm., and hence the polypary is decidedly 

 broader. 



Horizon and Localities. — Llandovery (zones of 

 M. gregarius and M. convolutus.) 



S. Scotland: Dobb's Linn. Wales : Rheidol 

 Gorge, 430 yds. S.S.E. Bryn-chwith Farm, Pont 

 Erywcl. 



Collections. — Geological Survey of England and 

 Wales, and of Scotland, Sedgwick Museum, Lap- 

 worth. 



Proximal thecse. Enlargement of part 

 of PI. XLIX, tig. 2 b. 



Monograptus fimbriatus (Nicholson) 



Plate XLVIII, figs. 4 a—d. 



1868. Graptolites fimbriatus, Nicholson, Quart. Journ. Geol. See, vol. xxiv, p. 536, pi. xx, figs. 3 — 5. 



Figs. 338 a and b. — Monograptus fimbriatus 

 (Nicholson). 



Polypary small but relatively broad, arcuate, with circinate proximal portion, 

 widening quickly to a maximum breadth of 1*8 mm. Thecas on the convex 

 margin, twelve to nine in It) mm., those of the proximal portion somewhat 

 more slender than those of the more distal portion, which also have blunter 

 reflexed apertural terminations in which the merest fraction of the thecal 

 length is involved. 

 Description. — The polypary does not usually exceed 4 cm. in length, and 



smaller forms are of far commoner occur- 

 rence ; the circulation of the proximal portion 

 is always pronounced. 



The sicula is small, barely reaching 1 

 mm. in length. 



The thecae of the initial portion are 

 rather different from those developed later, 

 they are distant, relatively long, slender, and 

 triangular in form, with sharply reflexed 

 apertural regions ; they change gradually in 

 shape, however, becoming closer set, shorter 

 and broader, with more bluntly reflexed 

 apertural regions. This latter type is the 

 characteristic fimbriatus type, while the 

 earlier theca? appear to approach those of 

 M. triangulatus. It is not clear, however, whether the difference in the form of 

 the proximal and distal thecas is not merely an appearance due to torsion. Should 



a. Proximal fragment, preserved as a cast, show- 

 ing sicula. Skelgill, Lake District. Coll. 

 Lapworth (presented by H. A. Nicholson). 

 . Proximal fragment in relief. Skelgill, Lake 

 District ; Skelgill Beds. Coll. Lapworth. 



