472 BRITISH GRAPTOLITES. 



Th. 2 is similar in form but snorter. Thus far the polypary is extremely slender, 

 but thereafter increases gradually in breath, and the thecae continue to increase in 

 length until the maximum breadth is attained. 



The thecas are commonly preserved to show merely acutely pointed apices, but 

 here and there one may be detected with the characteristic barbed apertural 

 region, and in specimens preserved in relief the barbs are usually quite clearly seen, 

 though only a small fraction of the thecal length is involved in their formation. 



Affinities.— Moriog. triangulatus is a very Avell marked species; proximal frag- 

 ments might perhaps be confused with those of M. fimbriatus or M. communis, but 

 the linear-triangulate distal thecal should render the identification of mature 

 specimens comparatively easy. 



Horizoii anil Localities. — Llandovery (zone of M. gregarius). 



S. Scotland: Dobb's Linn ; Belcraig Burn ; Frenchland Burn ; Lockerbie, etc. 

 Lake District: Skelgill ; Spengill Head, etc. Ireland: Coalpit Bay, Donaghadee; 

 Little River, Pomeroy ; Side Valley, Mullaghnabuoyah, Pomeroy. Wales : Mona 

 Aline, Parys Mountain; Rheidol Gorge, loO yds. S.S.E. Bryn-chwith Farm, Pont 

 Erwyd, etc. 



Associates, etc. — Mo nog. triangulatus is one of the very commonest fossils in the 

 M. gregarius zone ; it usually makes its appearance at the base associated with M. 

 gregarius, M. finibriatus, Rastrites approximates, Mesog. magnus, Olimacog. Tornquisti, 

 etc., and continues up to the very summit of the zone. 



Collections. — British Museum (Natural History), Sedgwick Museum, Geological 

 Survey of England and Wales, and of Scotland, Kelvingrove Museum, Glasgow, 

 Lapworth, Jones, and the Authors. 



Var. major, var. nov. Plate XL VII, figs. 5 a — J. 



FiG S .328aandb.-Jifo»o ? m^(ts<,-iaH i ,K- Xi the top of the zone of M. qreqa rins there 



latus, var. major, nov. L 



commonly appears a variety of M. triangulatus, in 



which the curvature is, as a rule, broader, and the 



JiL"Y jg? ^^xY' thecae much longer than in the typical form, 



*<s^' c^ k I approximately seven-eighths of the total length 



V> 



^"jr ' being isolate, though the relative fraction involved in 



*y.,_^sf ~^» ~ V; \ the barb remains the same. This increase in length 



of the thecae makes the whole polypary of greater 



a. Proximal fragment, showing sieuia. breadth, and the appearance of the polypary is 



SaS HistoryMSeum. ^^ altogether more robust, while the thecas are some- 



b. Distal fragment preserved as a cast. j fc j t numbering twelve to Seven ill 10 



Same locality as PI. XLV11, tig. o c. o 



mm., and having a length of 2*5 to 3 mm. The 

 sicula also is longer, measuring 1*5 mm. in length. 



Horizoii and Localities. — Llandovery (zone of M. gregarius, especially upper part). 



