MONOGRAPTUS. 



481 



Fiii.-i. ;i;s(S a and b. — Monograptus com- 

 munis (Lapworth). 



\ 



i 



& 







a. Proximal fragment, in relief, pro- 

 bably belonging to this species. 

 430 yds. S.S.E. of Bryn-chwiih 

 Farmhouse, Pont Erwyd, Cardigan- 

 shire. Geol. Survey of England 

 and Wales. 



6. Distal thecae, showing different ap- 

 pearances presented after compres- 

 sion. Ladhope Burn, Galashiels ; 

 Birkhill Shales. 

 Scotland. 



pression and method of preservation ; even when 

 seen their appearance is very variable, but usually 

 some thecae show the characteristic form even when 

 very much compressed, and in specimens preserved 

 in relief their true shape is usually seen very 

 beautifully. 



Affinities. — It is clear that in Monog. communis 

 we have a form in which the thecae are in many 

 respects intermediate in character between those 

 considered as typical of the group of M. lob&fevws 

 and those typical of the group of M. convolutus ; 

 especially is this the case as regards the apertural 

 region, which strongly recalls the lobate form of 

 many members of the group of M. lobiferus. 

 Nevertheless the general triangular shape of its 

 thecae and their greater degree of isolation seem on 

 Geoi. Survey of ^he wno l e to link it even more closely with the 

 members of the group of M. convolutus, among 

 which it is here consequently included. 



Monog. communis might be confused as regards its distal portion with the similar 

 portion of M. Glingaui, but may be distinguished by the more overlapping thecae 

 and the more hooked apertural regions of the latter species. From M. millepeda, 

 to which it bears a close resemblance in the form of the polypary, it may be 

 separated by the less definitely lobate nature of the apertural regions. 



Horizon and Localities. — 'Llandovery (zones of M. gregarius and M. convolutus). 

 S. Scotland : Dobb's Linn ; Belcraig Burn ; Garple Linn ; Frenchland Burn ; 

 Lockerbie, etc. Wales : Rheidol Gorge, 430 yds. S.S.E. Bryn-chwith Farm, Pont 

 Erwyd, etc. Lake District : Skelgill. Ireland: Little River, Pomeroy. 



Associates, etc. — Monog. com munis is a common fossil in the lower part of the 

 Upper Birkhill Shales of S. Scotland and their equivalents elsewhere ; it occurs 

 in association with M. gregarius, M. triangulatus, and var. major, M. Glingani, M. 

 convolutus, Petalog. folium, 1'. palmeus, Oephalog. cometa, etc. It is also fairly 

 common in Ireland and in the Lake District. 



Collections. — Geological Survey of England and Wales, and of Scotland, 

 Sedgwick Museum, British Museum (Natural History), Jones, Lapworth, and the 

 Authors. 



Var. rostratus, var. nov. Plate XLIX, figs. 2 a — c. 



This variety of Monog. comrmmis is very similar to the common form as regards 

 the shape of the polypary, but the theese are much longer and more rostrate, 



