374 



BRTTTRPI GEAPTOLITES. 



Figs. 2-1-1< a — d. — 3ro)ir>;irajiliis jiu-vhn)i 

 (Lapworlh). 



% 







fit orig'iii l)iit widoiiinii;' pcn'sistontly to a iiinxinuim brcadtli of about I'O mm. 

 Tbecse foTirtcen to uiuo in 10 mm., simple tul)es, overlap insignificant in tlie 

 proximal })ortion, but I'oacliiuo-a maximum of about one-half the total length 

 distally ; apertural margins Avide and even, generally more or less horizontal. 

 Descri.piion. — Tlie polypary may, and often does, attain a great length, luit 

 specimens with a length of only 8 or 4 cm. are of commonest occurrence. 



The sicvila is small, not exceeding v mm. in 

 length, l)ut reaching fnlly to the level of the aper- 

 ture of th. 1. 



The thecas in the proximal portion are very 



small and closely set, but become more distant 



^,^ towards the distal extremity of the polypary. The 



^1 ^1 _' _ npertural margins tend to be more or less hori- 



zont.il, i. e. perpendicular to the general trend of 

 the polypary, and occupy about one-third of the 

 total breadth of it in profile view. The mature 

 theca has a length of about 2"5 mm. 



Affinities. — -Monog. jnculum approaches M. rpr/u- 

 hiris in the characters of the proximal end and the 

 initial theca?, except that tliese are more closely set ; 

 in the distal portion, however, both the length of 

 the thecfe and their overlap are much less in the 

 former species. 



Horizon and Localities. — Llandovei-y (Birkhill 

 Shales), zones of M. /jregarins to ]\[. He<hjwicl-ii. 



/S'. iScotlaud : Dobl)'s Linn ; Belcraig Burn ; 



Garple Linn ; Lockerbie, etc. 6'. JValcs : Rheidol 



Gorge, etc. N. Wales: Llanystwnidwy ; Oonwaj^ 



etc. Irclaiiil : Coal])it Bay, Donnghadee; Limehill, Co. Tyrone; Little River, 



Pomeroy, Co. Tyrone, etc. Lal-e Distrirf : Skelgill; Long Sleddalc ; Tributary 



of Hall Gill, etc. 



Associates, etc. — Monog. jaculnvi is a very common fossil in the Upper Birkhill 

 Shales of Moffat and their equivalents elsewhere. It occurs associated with 

 Monog. gregaritis, M. leptathrca, M. Clivgani, M. coniniunis, M. conrolntns, M. 

 harpigo, M. incolntns, M. 8edg ivicldi, CepJialog. coineta, and many other forms. 



Collections. — Sedgwick Museum, Geological Surveys of England and AVnles, and 

 of Scotland, Jones, Lapworth, and the Authors. 



a. ri-oxiiiial end, showing part of sicula. 



Morioc'h Bay, ni-. Port I'atrick ; 



Birkhill Shales. Coll. Geol. Survey 



of Scotland. 

 h. Pro.xinial portion in relief. E. 



Yarrow ; Upper Birkhill Sliales 



(Band of Monograptus llalli). Coll. 



Lapwortli. 



c. Distal thecffi in relief. Ibid. 



d. More distal thecie, slightly com- 



pressed. Dobb's Linn, Upper Birk- 

 hill Sliales. Coll. Lapworth. 



Monograptus variabilis (Perner). Plate XXXVII, figs. 5 a, l>. 



1897. Monogniplus jaculvm, var. variabilis, Perner, jfitudew sur les Graj)t. de Bulicine, pt. iii, p. 12, 

 pi. xiii, figs. 10, 11—1.5. 



