MONOGRAPTUS. 



491 



Monograptus (Rastrites) hybridus (Lap worth). Plato L, figs. 4 a — -/. 



1876. Bastrites peregrinus, var. hybridus, Lapworth, G-eol. Mag. [2], vol. iii, p. 313, pi. x, fig. 5. 

 1892. Eastrites hyhridvs, Tornquist, SiljansomrM. Grapt., ii, p. 4, pi. i, fig. 2. 



1907. Rasfrites peregrinus, var. hybridus, Tornquist, Eastrites and allied species of Monograptus, 

 Lunds Univ. Arsskr., n.s., afd. 2, iii, no. 5, p. 7, pi. i, figs. 23, 24. 



Figs. 346 a andb. — Monograptus (Eastrites) 

 hybridus (Lapworth). 



Polypary small, arcuate, with broadly recurved proximal end. Thecte on the 

 convex margin, eight to ten in 10 mm., 2 mm. only in length, with narrow 

 interspaces, slightly declined, and with markedly reflexed apertural ex- 

 tremities constituting a well-defined barb. 

 Descriijtion. — The polypary never seems to attain any considerable size, and 

 the tliecEe are always rather short, and appear relatively closely set except in the 



proximal region, where tliey are shorter than 

 those developed subsequently. 



The sicula measures barely 1 mm. in length, 

 and there is a distance of 1"2 mm. between th. 1 

 and th. 2, and of 1'5 mm. between th. 2 and th. 3 ; 

 thereafter the thecee are barely 1 mm. apart, and 

 have an average length of 2 mm. 



The apertural barb is occasionally replaced 

 by two terminal thread-like processes. Tornquist 

 appears to consider the possession of these threads 

 a specific character {R. 'pUleoides). We are unable 

 to satisfy ourselves that this is so, since we have 

 discovered them in more than one species, and 

 it seems to us possible that any Eastrites might 

 show a " phleoid " development. 



Affinities. — Though fragments of Monog. (//.) 

 hybridus bear a considerable resemblance to those 

 of M. (B.) peregrinus, the character of the proximal end and the very pronounced 

 barb make this species distinct. 



Horizon and Localities. — Llandovery (zones of M. convolutus and M. Sedgwicki). 

 8. Scotland : Dobb's Linn ; Belcraig Burn ; Meggat Water. Lalce District : 

 Skelgill. C. Wales: 2 miles E.N.E. Pont Erwyd ; E. side of Quarry N.E. of 

 Fagwr-Fawr Farm. 



Associates, etc. — Monog. {B.) Ityhridiis occurs somewhat plentifully in the zone 

 of M. convolntns, where it is found associated with the zone-fossil, M. Glingani, M. 

 decipiens, M. intermedius var. involutus, M. lohiferus and other forms ; and also in 

 the zone of ilf. Sedgwlckl with M. SedgwicH and M. jaculum. 



a. Proximal portion in part relief, showing 



sicula. Enlargement of part of PI. L, 



fig. 4 c. 

 h. Proximal and distal thecse. Eheidol 



Gorge, Pont Erwyd, Cardiganshire. Geol. 



Survey of England and Wales. 



