452 



B RITIS H G R APTO LIT E S . 



Figs. 310 a — c. — Monograptus runci- 

 natvs var. pertinax, var. nov. 





6 



a. Proximal portion with sicula, partly 



in relief, partly a cast. Enlarge- 

 ment of part of PI. XLV, fig. 3 a. 



b. More distal fchec®, in relief ; reverse 



aspeet with apertural margins 

 partly turned away. Enlargement 

 of part of PI. XLV, fig. 3 b. 



c. Distal thecae, in relief; obverse 



aspect, with apertural margins 

 partly facing. Gelli-dywyll Stream, 

 Llanbrynmair ■, Brvnmair Beds. 

 Coll. Wood. 



Figs. 311 a and b. — Monograptus Becki 

 ( Barrande). 



a. Proximal portion. Enlargement of 



part of PI. XLV, fig. ia. 



b. Distal thecse, showing extreme retro- 



version of apertural regions. En- 

 largement of part of PI. XLV, fig. 

 4 d. 



too, the thecae are less closely set in the proximal 

 portion of the polypary, measuring ten in 10 mm. 

 against eleven in M. runcinatus itself, while the 

 thecal walls are as a rule more conspicuous. 



HmHzoli and Localities. — Gala-Tarannon Beds 

 (zone of M. tumculatus). 



Wales: Gelli-dywyll Stream, below Farmhouse, 

 and Gelli Stream, near Llanbrynmair. Scotland: 

 Buckholmside, Galashiels. 



Collections. — Geological Survey of Scotland, and 

 Wood. 



Monograptus Becki (Barrande). Plate XLV, figs. 



4 ft—/. 



1850. Graptolithus Becki, Barrande, Grapt. de Boheme, p. 50, 



pi. iii, fig. 14. 

 187<">. Monograptus Becki, Lapworth, G-eol. Mag. [2], vol. iii, 



p. 500, pi. xx, figs. 2 (7, b. 



Polypary several cm. in length, arcuate or 

 irregularly flexed proximally, widening very 

 gradually from a slender thread-like proximal 

 portion till a maximum breadth of 1 mm. is 

 attained. Thecas usually on concave margin, 

 ten in 10 mm., of the M. lob/fern* type. 

 Description. — The irregularly flexed or arcuate 

 form of the polypary with the theca? on the concave 

 margin, and the persistently increasing breadth are. 

 characteristic of the species. 



The sicula is unknown. The thecae in the 

 proximal portion are very slender, the only conspic- 

 uous feature being their lobes. The theca? increase 

 in size distally until they have a very characteristic 

 shape, their outer vails forming an almost straight 

 line down the polypary, broken only by the apertural 

 lobes (Fig. oil l>). The lobes themselves are coiled 

 completely round and are somewhat twisted, so that 

 they closely resemble those of 3f. lohiferus though 

 the adnate region of the thecae is rather more 

 conspicuous. 



