428 



BRITISH GRAPTOLITES. 



Figs. 290 a and b. — Monograptus 

 uncinatus var. orbatus, Wood. 



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colon us. Indeed, the whole proximal portion of the polypary resembles that of 

 an M. colon us in which the proximal type of theca persists for a greater distance 

 than usual. 



In the distal portion of M. uncinatus var. orbatus, 

 however, as the result of compression, a peculiar 

 appearance is seen, due to the combined effect of 

 greater torsion of the theca and its more distinct 

 claw-like or spine termination in the apertural 

 region. Such an appearance is shown in fig. 290 b, 

 and also in var. microjpoma, fig. 291 a. 



Affinities. — The combination of a colonus-like 

 shape of the polypary with a general Fleming ii-like 

 type of theca? is characteristic of this form, which 

 seems to be the British representative of the Swedish 

 M. uncinatus. From the variety micropoma , the 

 only graptolite to which the form under descrip- 

 tion approaches closely both in the form and the 

 characters of the thecae, it differs in being wider, in 

 having more thecas in the same unit of length, and 

 a rather more conspicuous beak. 



Horizon and Localities. — Lower Ludlow Shales 

 (zone of M. Nilssoni). 

 Welsh Borders: Trefnant-Middletown Brook, Long Mountain. Worcestershire: 

 Wren's Nest, Dudley. 



Associates, etc. — Monog. uncinatus var. orbatus is a rather rare fossil in the 

 Lower Ludlow Shales, where it occurs in the zone of M. Nilssoni with the 

 following characteristic assemblage: M. boltemicus, 3f. Nilssoni, M. vulgaris and 

 M. varians. 



Collections. — Dr. Fraser, Wood. 



a. Proximal end, showing part of sicula. 



Trefnant-Middletown Brook, Long 1 

 Mountain ; Lower Ludlow Shales. 

 Coll. Wood. 



b. Distal thecae, showing different ap- 



pearances presented after com- 

 pression. Enlargement of part of 

 PL XLIII, fig. 1 c. 



Var. micropoma (Jaekel). Plate XLIII, figs. 2 a — c. 



1889. Pomatoyraprtus micropoma, Jaekel, Zeitsclir. cT. deutscli. geol. Gesell., vol. xli, pi. xxix, figs. 



4—6. 

 1900. Monograptus uncinatus var. micropoma, Wood, Quart. Journ. Geol. Soc, vol. lvi, p. 477, pi. xxv, 



figs. 24 A and B, text-figs. 21 a and b. 



In addition to the variety described above, there occurs somewhat rarely in 

 Britain another closely allied form which it seems best to regard as another variety 

 of M. uncinatus. This is Jaekel's Pomatog. m icropoma, which differs from var. orbatus 

 in being rather straighter, in having a maximum breadth of 1"3 mm., and in having 



