372 



BRITISH GRAPTOLITES. 



theca, Lapworth. 



j[()im(ics. — The very long t^lellder thecvo Avitli their great overlap are highly 

 characteristic of this species, the only forms approaching it in this respect being 

 Figs. 242 a—c.—Monograptus hpio- M. achuices and M. ro(jnlavis. In M. aciiiaces, how- 

 ever, the distal tliecte are more trumpet-shaped and 

 the overlap is not so great, while in M. regularly 

 the overlap is also less and the proximal end of the 

 polypary is stiff and straight like the distal termi- 

 nation. 



Ilorizoit and Localities. — Llandovery (Birkhill 

 Shales), zones of 71/. (jrcgarlns to ilf. Sedgwickii. 

 S. Scotlaiul : Dobb's Linn ; Belcraig Burn ; 

 « ^\;: IM Frenchland Burn, etc. 0. IF^^Zt'^' .- Rhayader ; llhei- 



^ m tfi '^"^ Gorge; River Twymyn. N. Wales: Pary's 



■^1^ \\S:l I'''// Mountain, Anglesea; Llanystwmdwy. Lalce Dis- 



trict : Skelgill ; W. side Long Sleddale ; Stile End ; 

 Whinny Gill, Cross How Beck. 



Associates, etc. — Moiiog. Icptotheca seems to make 



its first appearance in the zone of M. gregnrins 



fipu;ed Lapworth. Geo] Mag., 1S76, al)ont the horizoii of the 71/. an/euteiis band, in 



pi. XII, fig. 4 e. Dolib .s Linn ; Bnk- '' ' 



hill Shales. Coll. Lapworth. Avhicli it is vcry common. It is also fairly abundant 



in the zone of 71/. convolutiis and survives into the zone of 71/. Sedgiviclii. It is 

 commonly associated with Monog. avgenteus, var. ci/gvevs, 71/ grcgarins and 71/. 

 rndtepeda. at the lower horizon, with 71/. convolntm^, M. involiitns and 71/ Jiacjuigo 

 in the 71/ conroliitiis zone, and with 7lf. tenuis and 71/ SedgiricJrii, in the zone of 

 71/. Sedgwickii. 



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

 Sedgwick Museum, Jones, Greenly, Lapworth, and the Authors. 



a. Thecse of the proximal portion of the 

 polypary, part i)res('rved as a cast, 

 part in ri'lief. Enlargement of part 

 of PI. XXXVlLfig. 2 6. 



h. More distal part of s;inie speeimen. 



r. Distal theca\ preserved as a cast, 



Monograptus regularis, Toriujuist. 



Plate XXXVII, figs. 3 (^— ^^ 



1899. Monoyra^ifvs rcgvJarix, Toiiiqiiist, Monograjitidse of Scaiiian Raatrites Beds, Luuds Uuiv. 

 Arssk., vol. XXXV, jit. 2, no. 1, p. 7, pi. i, figs. 9 — 14. 



Polypai-y several cm. in length, straight and approximately rigid throughout, 

 widening persistently from an initial breadth of about '3 mm. till the 

 maximum width of 1'5 mm. is attained. Thecse twelve to eight in 10 mm., 

 simple tubes overlapping but slightly in the proximal portion, but overlap 

 increasing to two-thirds of total length distally ; apertural margins wide, 

 even, slightly everted. 



Description. — The polypary is often very long, and the increase in breadth in 

 the proximal portion is so gradual as to be scarcely perceptible. 



