484 



BRITISH GRAPTOLITES. 



Horizon and Localities. — Llandovery (base of zone of M. (jregarius). 



8. Scotland: Dobb's Linn; Frenchland Burn; etc. Lake District : Skelgill. 

 Ireland: Donaghadee. 



Associates, etc. — Var. similis is found on approximately the same horizon as 

 the typical form and with the same associates, but is commoner in Scotland and 

 rarer in the Lake District. 



Collections. — Sedgwick Museum, Marr, Lapworth, and the Authors. 



Monograptus planus (Barrande). Plate XLVIIT, figs. 6 a — d. 



18-50. GraptoUthus protms var. plana, Barrande, Grapt. de Bolu-rae, p. 58, pi. 4, fig. 15. 

 1879. Monogmptm resurgens, Lirmarsson, G-otlands Grapt., p. 515, pi. 23, fig. 13 — 21. 



Fig. 340. — Monograptus planus 

 (Barrande). 



Polypary small, not exceeding 2 cm. in length, arcuate, with recurved proximal 

 portion, widening rapidly from a slender initial part to a maximum breadth 

 of about 1 mm. Theca? fourteen to twelve in 10 mm., of uniform type, 

 subtriangular, in contact only, with a considerable fraction of the free 

 region involved in an apertural barb. 



Description. — The rapid widening of the poly- 

 pary is very characteristic of the species, and the 

 proximal end is never enrolled as in those species 

 which it slightly resembles. 



The thecas, though smaller in the proximal than 

 in the distal portion, are never inconspicuous ; the 

 apertural barb is, however, fairly frequently con- 

 cealed, and the thecas then present a bluntly 

 triangular appearance. 



Affinities. — Manor/. planus agrees in some respects 

 with M. decijiiens, and distal fragments of the two 

 species resemble each other somewhat closely, 

 though the thecas in M. decipiens are more distant 

 than those of M. planus. Their proximal ends are, 

 however, quite different, that of M. planus being merely recurved and not enrolled, 

 while there is no sign of the Rastrites-like proximal thecas so characteristic of M. 

 drcipiens. Monog. planus reminds one of a M. spiralis in which the curvature is 

 arcuate rather than spiral. 



Horizon and Localities. — Grala-Tarannon beds (throughout). 

 Lake District: Hebblethwaite Gill. Scotland: Allan Water, nearly opposite 

 Avernel Plantation, 3 miles N.W. of Melrose. Wales: Tarannon River; Plas- 

 bach stream, near Llanbrvnmair, etc. 



Thecae in full relief, preserved in three- 

 quarter face view at the distal end. 

 Enlargement of part of PI. XL VIII, 

 fi<r 6 o. 



