MONOGRAPTUS. 393 



to twelve in ]0 mm.), and tlie polypary as a whole is somewhat longer and 

 narrower. 



Affinities. — Many different species of Graptolites have been erroneously 

 referred to Barrande's species Mmiog. colomis ; of these the commonest were those 

 later described l:»y Wood as M. viilgnris, 3/. tumescpns, and M. rarians (loc. cit. 

 snpra). In all four species the distal thecae resemble each other very closely, but 

 the proximal thecae and the general characters of the proximal end are different. 

 From M. vulgaris, M. coJoniis differs in the curved proximal end and in the 

 characters of the proximal thecae, from M. tvmpscens in the characters of the 

 proximal thecse, and from M. varians in its wider polypary and somewhat different 

 distal thecae with their greater overlap. 



Horizon and Localitios. — Lower Ludlow Shales (zone of M. Nilssonl). 



Lalce Disfricl : Helm Knot, Dent; N.E. Casterton Fell. N. Wales: Deeside 

 Slab Quarries, Moel Ferna ; Hills N.E. Llanrwst ; R. bank of Dee, Llangollen, 

 etc. Wplsh Borders: High Cliff, R. L-fon, near Builtli ; Vicarage Road, 

 Builth, etc. Liidloiv District : Elton Lane ; Adferton ; Trippleton Lane ; Bow 

 Bridge, etc. 



Associates, etc. — Moiiog. colonns is a fairly abundant fossil in the Lower Ludlow 

 Shales where the Mudstone facies is best developed, as it is in the Builtli District ; 

 elsewhere it is by no means so abundant as has generally been supposed, though 

 it is essentially a characteristic fossil of the lower part of those shales. It occurs 

 typically in the zone of M. Nilssoni, and is usually to be found in association with 

 the zone fossil, 7)/. hohemicns, 3f. duhins, and Gothog. spinosns. 



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

 Lapworth, and the Authors, etc. 



Var. compactus AYood. Plate XXXVIII, figs. 10 



a- — c. 



V>.v- 



1900. Monograpiiis colonns, var. compacivs, Wood, Quart. Joiirn. Geol. Soc, vol. Ivi, p. 466, pi. xxv, 

 fig. 12. 



Fig. 261.— Monograptus coionvs, var. ^ well-marked Variety of M. colonns has been 



compactus, Wood. _ "^ 



appropriately termed var. compactus. This agrees 



with the typical Movog. colonns in the shape of the 



thecfB and character of the proximal extremity, but 



^ ■ 'l^ is distinguished from it (1) by its smaller size (not 



'^'..y exceeding 2*5 cm. in length) and more decided 



^^^n curvature ; (2) by the densely set thecse (sixteen 



■^S;-^--..; to fourteen in 10 mm.), which may overlap as much 



yv%; I as three-quarters of their length in the distal portion 



of the polypary. The virgula is conspicuously 



Distal thecae. Enlarffement of pait of -, -, ^ -i ,^ -<• , ^ -> f ,i i 



PI. xxxviii, fig 10a. prolonged beyond the distal end or the polypary. 



