106 



BRITISH GRAPTOLITES. 



Figs. 238 a ami h. — Monngrapttis gre- 

 garius, Lapw. 



rolyiiai-y short, arcuate, Avitli an average length of ■) cm. and uniform breadtli 

 of abont "75 mm. Sicnla very conspicuous and of great length. Thecee 

 ten in 10 mm., simple tubes "with even apcrtural margins lying perpen- 

 dicularly to the general trend of the polypary, overlap increasing from 

 mere contact to one-third of thecal length. 

 Description. — The gregarious habit of this species is highly characteristic, slabs 

 of I'ock being covered with its small stiffly curved polyparies. 



The proximal end appears unusually robust on account of the extent and 



size of the sicnla, which measures fully 5 mm. in 

 leugtli, and which reaches up to the level of the 

 aperture of th. 5, whence it gradually merges into 

 the virgula; since th. 1 arises a little distance 

 above the aperture of the sicnla, the sicula together 

 with five theca& form tlie proximal portion of the 

 polypary. 



The thecae show a distinct tendency to expand 

 in the direction of the aperture. 



Affimties. — The stiffly curved polypary and the 

 robust character of the proximal end, together with 

 the disposition of the relatively gigantic sicula, 

 sho\dd serve readily to separate this species from 

 .any other Mo7iograptns. Distal fragments, how- 

 ever, have sometimes a superficial resemblance to 

 " ^ those of M. intermedins when badly preserved, 



a. Proximal cn.i.showinj,^ sicula. D.^.i.'s tliough the tlicca? of the latter species are different 



Linn ; Mill. Biikhill Shales. Coll. o '^ 



Lapwoith. ,. , , . . , in form. 



0. SiJCCMiiien in reliel, showing sicula. 



ibi'l.? Horizon and Localities. — Llandovery (Birkhill 



Shales), zone of M. grcgarius. 



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

 etc. N. Ireland: Coalpit Bay, Donaghadee ; Wales: Twymyn River, near 

 Llanbrynmair ; Rhayader; etc.; Pont Erwyd ; etc. LaJce District: Skelgill ; 

 Browgill; Stile End. 



Associates, etc. — Monog. gregarius is one of the commonest fossils in the 

 Llandovery wherever the graptolitic facies is developed; it occurs in swarms as a 

 general ride, and is often associated with Monog. fimhriatiis, M. communis, M. 

 triangvdatus, Bastrites appvoxhnaius, Glj/j^tog. si mm fits, G. tamariscns, Cliinacog. 

 Tornquisti and other forms. 



Collections. — Geological Survey of Scotland, Sedgwick Museum, British 

 Museum (Natural History), Lapworth, Fearnsides, Jones, and the Authors, etc. 



