480 BRITISH GRAPTOLITES. 



fig. 335.— Monographs drcuUHs, s P . The thecse, although somewhat smaller, resemble 



nov 



in all other particulars those of M. communis, and 

 there is no sign of the rapid increase in size of the 



distal thecse so characteristic of M. sjrirah*. 



Affinities. — Monog. circularis agrees with M. 



convolutus and M. spiralis in general form, but may 



readily be distinguished from these by the different 



characters of the thecas. From M. communis, with 



Enlargement of part of pi. xlviii, fig. which it agrees in the shape of the thecge, it differs 



9 a. 



completely in the form of the polypary. 

 Horizon and Localities. — Llandovery (zone of M. Sedgwickii). 

 S. Scotland: Pie wlands Burn, Raehills (Duffkinnell) ; the Corrie, Dobb's Linn. 

 Associates, etc. — Monog. circularis is a rather rare fossil in the Upper Birkhill 

 Shales, "where it occurs with M. Sedgwiclm and M. jacnhun. 

 Collections. — Geological Survey of Scotland, and Elles. 



VI. B. (b) : Monograpti in which the thecse are uniform and the polypary has 



dorsal curvature. 



Monograptus communis (Lapworth). Plate XLIX, figs. 1 a — e. 



1876. Monograplus convolutus var. communis, Lapworth, Geol. Mag. [2], vol. iii, p. 358, pi. xiii, 

 figs. 4 a, b. 



Polypary 5-8 cm. or more in length, arcuate or straight distally, with sharply 



recurved proximal portion, widening rapidly to a maximum breadth of 



1"4 mm., which is uniformly maintained throughout the distal portion. 



Theca3 eight in 10 mm., on the convex margin, in contact only, short, broadly 



triangular, free seven-twelfths of length, with reflexed almost lobate apertural 



regions in which one-third of the total thecal length is involved. 



Description. — The curvature of the polypary varies considerably in different 



individuals. Sometimes it is arcuate throughout, sometimes with broadly, sometimes 



with narrowly, recurved proximal portion, while the distal portion may be nearly 



straight. 



The sicula has a length of 1*2 mm. and the early thecas are apparently very 

 small, but this appearance is due to the fact that they are elongated and 

 narrow, with less conspicuous apertural regions ; th. 1 seems to have a length of 

 fully 1*5 mm. 



The reflexed apertural regions of the thecas are not always Avell shown, partly 

 as the result of slight torsion of the thecal axes, and partly as the result of com- 



