474 BRITISH GRAPTOLITES. 



Horizon and Localities. — Llandovery (zone of M. gregarius, near base). 



S. Scotland: Long Linn, Dobb's Linn. Wales : Rheidol Gorge, 4o0 yds 

 S.S.E. Bryn-chwith Farm, Pont Erwyd. Lake District : Skelgill ? 



Associates, etc. — -Monog. raitzhainiensis seems to be one of the earliest of all the 

 members of this group ; it makes its appearance at the very base of the zone of 

 M. gregarius immediately above the zone of M. cyphus ; here it occurs in associa- 

 tion with M. fimbria tits, M. revolutus, M. Savdersoni, M. gregarius, Olimacog. Tbrn- 

 quisti, -Rastrites approximatus, Petalog. palmeus var. latus, etc. Jones has also found 

 it, at a slightly higher horizon, in his M. communis zone {Mesog. mar/mis band) 

 with M. communis, M. gregarius, Mesog. mat/mis, GUmacog. Tornquisti, and Ras- 

 trites approximatus. 



Collections. — Jones, Geological Survey of England and Wales, Sedgwick 

 Museum, Elles. 



Monograptus denticulatus, Tornquist. Plate XL VIII, figs. 2 a — /. 



1899. Monograptus denticulatus, Tornquist, Monog. of Scanian Rastrites beds, p. 18, pi. iii, figs. 

 19—23. 



Polypary small, not exceeding 4 cm. in length, and commonly even smaller, 

 arcuate, with broadly recurved proximal portion widening quickly from 

 an initial breadth of about '7 mm. to a maximum diameter of 1*3 mm. 

 Thecas on the convex margin, eight to nine in 10 mm. ; those of the proximal 

 portion of the M. triangulatus type, those of the distal portion of the general 

 M. communis type. 



Description. — -The polypary is usually small, but longer specimens are occasion- 

 ally met with, all showing considerable variation in 



Fig. 330. — Monograptus denticulatus, ,i ...... „ 1 • i i 



Tornquist. the amount of circulation or the proximal end. 



iy The sicula has a length of about 1 mm. and 



forms the proximal termination of the polypary, 

 n th. 1 arising: some distance above its base. 



N The two distinct types of thecas are highly 



characteristic and very conspicuous, those of the 

 proximal portion being linear-triangulate in form, 

 while those of the distal portion widen out till they 

 K come to resemble those of M. communis, though 



with a rather less conspicuously re flexed apertural 

 Proximal portion Enlargement of part region. As Tornquist has already noted, the 



of PL XLVIII, fig.2l. => . ' •; . 



combined effect of compression and slight torsion ot 

 the thecal axis results in curious views being presented. One of the most misleading 



