MONOGRAPTUS. 



377 



1890. Monographis cluhius. Holm, Grotlands Grraptoliter, Bihang till k. Svensk. Yet. Akiid. Haudl., 



vol. xvi, pt. iv, no. 7, p. 16, pi. i, figs. 18 — 26. 

 1893. Monograptus duhiiis, Wiiuan, Bull. Geol. Inst. Upsala, vol. i, no. 2, p. 2, pi. vii. 

 1900. Monocjrapins diihins, Wood. Quart. Jouru. Geol. Soc, vol. hi, p. 454, pi. xxv, figs. 1 a, 1 b. 



tcxt-fiu-. 9. 



Figs. 247 a and h. — Mimograptus duhins 

 (Suess.). ■ 



Polypary with a maximum length of 10 cm., straight distallj, Ijut with slight 

 ventral curvature in the proximal portion, widening gradually till maxinuim 

 breadth of 2 mm. is attained. Theca3 eleven to eiglit in 10 mm., fairly 

 long and wide tubes two or three times as long as Avide, overlapping from 

 less than one-half to rather more than one-half their length ; average 

 inclination 30° — 35". 

 I)escrij)tioii. — The pol3q)ary varies considerably in extent; at some horizons in 

 the Wenlock Shales it I'arely exceeds 4 cm. in length, and seldom attains the 



maximum breadth ; whilst in the Lower laidlow 

 Shales it is frequently 10 cm. long ; in all other 

 respects, however, the examples from both forma- 

 tions agree exactly. The slight ventral curvature 

 of the proximal portion in the neighbourhood of 

 the conspicuous sicula is highly characteristic ; it 

 rarely involves more than six thecas. 



The sicula has a length of 1'7 mm. and is about 

 four and a half times as long as wide; its apex 

 reaches approximately to the level of the second 

 thecal aperture. 



The i^roportions of the distal thecffi are fairly 

 constant ; the apertural margins are even but fre- 

 quently somewhat thickened to form a sort of 

 flange, which gives rise to a blunt denticle after 

 compression. The average length of the mature 

 thecce is 3 mm. 



Affinities.- — Mojtcxj. dnhius somewhat resembles 

 in its general characters both M. vulgaris and M. 

 tumescens, but should be readily distinguished from the former by the proximal 

 ventral curvature, and from the latter by the shorter broader thecjB. It has 

 often been confused with Jl/. colonus, but the two are easily separated owing to the 

 absence in M. (hihiiis of any retroversion of the thecse such as is characteristic 

 of the proximal end of M. cohniiis. 



Horizon and Localities. — Wenlock — Ludlow (zone of M. riccartonensis to zone 

 of M. scanicus). 



S. Scothnid, : Eiccarton ; Hindhope, etc. LaJrc District ; Moughton ; Whetstone 

 Hole; beloW' Rother Bridge, etc. Welsli Borders : Walcot Quarry, Chirbury; Coed 



if- 



1 



a. Proximal end, sliowino^ sicnla. En- 

 largement of part of PI. XXXVII, 

 fig-. 7 a. 



h. Distal thecse, part in low relief. En- 

 laro-enient of part of PI. XXXVII, 

 fiff. 7 b. 



