MONOGRAITrS. 



479 



Figs. 334 a — c.—Monograptus involutus 

 (Lap worth). 



Polypary an involute plane spiral of somewhat irregular form, with slender 

 thread-like proximal portion, and widening fairly rapidly to a maximum 

 diameter of rather less than 1 mm. Theca3 on the outer side of the curve, 

 eight in 10 mm., of the type characteristic of M. communis, but somewhat 

 smaller. 

 Description. — The irregular involutions of the polypary are highly distinctive 



of the species, though the amount of curvature 

 varies very much in different individuals. 



The proximal portion is very slender and the 

 thecae minute, so that it is difficult to make out the 

 details. The distal thecas present many different 

 appearances under compression, but are generally of 

 the type of those of M. communis. 



Affinities. — As regards the form of the polypary 

 Munog. involutus approaches M. delicatulus, but is 

 still more irregularly curved. The theca? agree 

 very closely with those of M. communis, but in that 

 species the curvature of the polypary is quite 

 different. 

 a be Horizon and Localities. — Llaudovery (zones of 



a. Proximal thecse. Enlargement of M. COUVolutuS and M. Sedgwicliii) . 



b and c. Different appearances of the 8. Scotland : Dobb's Linn; Garple Linn; French- 



SFS^SBlSJSS' Blrk " land Burn; Belcraig Burn; Head of Pishnack 



Burn, Wee Queensbury ; Sundhope-on- Yarrow ; 



Glenkiln Burn. Wales : W. side Old Quarry, N.E. of Fagwr-fawr, Pont Erwyd. 



Ireland : Near Limehill, Co. Tyrone. Lake District .- Skelgill. 



Associates, etc. — Mono//, involutus is a fairly common fossil, and is found most 



abundantly in the zone of M. convolutus associated with M. leptotheca, M. lobiferus, 



M. convolutus and M. Clingani; it is also found, but more rarely, at the higher 



horizon with M. tenuis and if. Sedgwickii. 



Collections. — Geological Survey of England and Wales, Sedgwick Museum, 



Lapworth, and the Authors. 



% 



Monograptus circularis, sp. nov. Plate XLVIII, figs. \) a and b, 



Polypary slender, convolute, coiled into a plane spiral fairly regular in shape, 



of a uniform breadth of about 1 mm. Thecae eight in 10 mm., of the type 



of those of M. communis. 



Description. — The polypary is coiled in much the same way as the more 



regular forms of M. spiralis, but the curvature varies somewhat in different 



specimens. 



63 



