414 



BRITISH GRAPTOLITES. 



theca) render 

 Graptolites. 



MoiKxj. (jricstonicnsis a very 



distinct form amongst 



Britisli 



Figs. 280 a and h. — Monngraptus cf. 

 griestoniensis, Nicol. 



S^ 



Horizon and Localities. — Gala-Tarannon (zone of 

 M. griestoniensis) . 



S. Scotland: Grieston Quarry, near Innerleithen. 

 Wales: Rhayader; Talerddig Railway Cutting; Afon 

 Cwm Calch, near Talerddig; Tarannon River, etc. 



Associates, etc. — Monog. griestoniensis is a charac- 

 teristic fossil in the Tarannon Shales at a special 

 horizon, where it occurs associated with Moiiog. 

 Marri, M. cliscns, M. pviudon, M. nudus, and M. siih- 

 conicus. 



Collections. — Sedgwick Museum, Geological Sur- 

 vey of England and Wales, Lapworth, and the 

 Authors. 



Note. — In the Tarannon District there occurs a 

 form which is intermediate in character between 

 Mouog. griestoniensis and M. romerinus var. crenv- 

 latns (Plate XLI, figs. G a. and h). It is more rigid and widens more decidedly than 

 does M. griestoniensis ; at the same time it is distinctly more slender than the true 



var. creiiulatus. It may possibly prove to be a 

 distinct variety. 



This form occurs typically near the top of 

 the Talerddig Grits, not far below the zone of 

 var. crentdatiis. 



a. Portions near proximal end in relief. 



Enlargement of parts of PL XLI, 



fig. 6 n. 

 h. Distal theca?. Another part of same 



specimen. 



Figs. 281 a — e. — Monograptus crenularis, 

 Lapworth. 



Lv*' 



If''* 



h' 







Monograptus crenularis, Lapworth. 

 XLT, figs. 7 a—r. 



Plate 



i' 



;^i 



a. Proximal end, showing the lobate appear- 

 ance of the thecae. Enlargement of part 

 of PL XLI, fig. 7d. 



I. Similar specimen. Enlai-gement of part of 

 specimen on same slal) as Fig. 281 a. 



r. Adult thecce ; preserved as a slight impi-es- 

 sion. Enlargement of part of PI. XLI, 

 fig. 7 b. 



d. Thecoe; preserved partly in relief, partly as a 



cast. Enlargement of part of PI. XLI, 

 fig. 7 c. 



e. Theca; ; compressed. Part of specimen on 



same slab as Fig. 281 c. 



1880. Monograptus crenularis, Lapwortb, Aun. Mag. Nat. 

 Hist. [5], vol. V, p. 153, pi. iv, figs. 10 a— 10 c. 



Polypary long and slightly arcuate through- 

 out, widening very gradually from '5 mm. 

 to a maximum breadth of 1 mm. Thecse 

 twelve to ten in 10 mm., overlapping two 

 thirds their length, with slightly everted 

 apertural margins, appearing occa- 

 sionally within distinct excavations. 



Description. — The polypary is character- 

 istically slender, and the maximum breadth is 

 attained some distance from the proximal end. 



