MONOGRAPTUS. 



I :> 1 



d. Specimen partly in relief, partly a 



cast. Llanystwmdwy, near Cric- 

 cieth ; Llandovery Beds. Coll. 

 Fearnsides. 



e. Distal thecae in relief, showing charac- 



teristic appearance. Glenkiln Burn, 

 S. Scotland ; Upper Birkhill Shales. 

 Coll. Lapworth. 

 /. Distal thecse, preserved partly as a 

 cast. Ibid. 



figs. 309 &- ■/.- -Monograptus rund- region of the theca, and being slightly refcro- 



natus, Lapworth. ° ° ° J 



verted and twisted causes the plane of the 

 apertural margin to lie somewhat obliquely 

 with respect to the general trend of the 

 polypary. 

 Description. — The polypary is commonly some- 

 what curved (with the thecse on the concave margin 

 except at the extreme proximal end), though short 

 fragments appear fairly straight; it widens gradually 

 throughout its length till the maximum breadth is 

 attained. 



The sicula has a length of 1 mm., reaching 

 slightly beyond the level of the aperture of th. 1. 

 The whole proximal end of the polypary strongly 

 recalls that of M. Becki. 



The thecal of the distal end have a fairly long 

 lobed region occupying about one-third of the 

 breadth of the polypary. As a result of compression the ventral wall tends to 

 show double curvature and the apertural margin appears often to be very oblique ; 

 the upper Avail is, however, so rarely discernible that the thecae when viewed upside 

 down bear the strongest resemblance to those characteristic of a Dicellograptus or a 

 Monograptus of the argutus type. 



Affinities. — Monog. runcinatus resembles M. Becki very closely in its proximal 

 portion ; it, however, differs markedly in the characters of the distal thecae, and 

 this should render the separation of the two species comparatively easy. 

 Horizon and Localities. — Gala-Tarannon Beds (zone of M. turriculatus) . 

 . 8. Scotland: Mount Benger; Eklinhope ; Belcraig Bum, etc. Wales : Forge 

 Corner, Conway ; River Twymyn ; Llanbrynmair ; West side of Upper Quarry, 

 550 yds E. of Faches-gau Farm, etc., Pont Erwyd. Lake District: Browgill. 



Associates, etc. — Monog. runcinatus is a fairly common fossil in the basement 

 rocks of the Gala-Tarannon beds, where it occurs associated with Bastrites maximus, 

 l\. Lin nasi, M. turriculatus, M. nudus, M. derirorms, M. spiralis, etc. 



Collections.— Geological Survey of England and Wales, Fearnsides, Lapworth 

 and the Authors. 



Var. pertinax, var. nov. Plate XLV, figs. 3 a — g. 



1906. Monograptus runcinatus mut., Wood, Quart. Journ. Geol. Soc, vol. lxii, p. 644 et seq. 



In addition to the typical forms of M. r 



u nana 



tus, there have been found others 



which appear to differ mainly in being much stiffer and straighter. In addition, 



