MONOGRAPTUS. 



(.85 



Associates, etc. — Monog. planus occurs throughout the Gala-TaraimoE beds asso- 

 ciated with their characteristic fossils. 



Collections. — Geological Survey of Scotland, Sedgwick Museum, and Wood. 



Monograptus intermedius (Carruthers). Plate XLIX, figs. 3 a — c. 



1868. Graptolithus intermedius, Carruthers, Geol. Mag., vol. v, p. 126, pi. v, fig. 18. 



1872. Graptolithus acutus, Hopkinson, Geol. Mag., vol. ix, p. 504, pi. xii, fig. 4. 



1876. Monograptus intermedius, Lapwoith, Geol. Mag. [2], vol. iii, p. 316, pi. x, figs. 10 a — c. 



Figs 341 a — d. — Monograptus inter- 

 medius (Carruthers). 



/ 



/ 



Polypary several cm. in length, arcuate, proximal end with variable curvature, 

 usually stiffly recurved, very slender throughout, but widening gradually 

 and persistently till a maximum diameter of rather less than 1 mm. 

 is attained. Thecal borne on the convex margin, eight to ten in 10 mm., of 

 uniform type, subtriangular tubes free two-thirds of their length and with 

 apertural region sharply bent over into a small insignificant barb. Overlap 

 increasing distally. 

 Description. — The polypary is very slender and delicate throughout, often 

 measuring only '7 mm. or '8 mm. in breadth; the curvature of the proximal end 



is variable, being sometimes merely arcuate, at 

 others sharply recurved, with every gradation 

 between the two extremes. 



The thecas are of the same general type 

 throughout, but those of the initial portion are so 

 extremely slender that they would be almost in- 

 visible were it not for the barb of the apertural 

 region ; the amount of overlap increases somewhat 

 distally but is never anything but very slight. 

 When the polypary is somewhat twisted the aper- 

 tural barb is not visible and the thecas then appear 

 to have a somewhat acute denticle ; specimens 

 showing this mode of preservation are not at all 

 uncommon, and it would appear that it was upon 

 such forms that Hopkinson founded his species M. 

 acutus (fig. 341 b). 



Affinities. — The slender nature of the polypary 

 and the characters of the thecas serve to render 

 Monog. intermedius readily recognisable. In some respects, perhaps, it approaches 

 M. communis, both as regards general form and general thecal characteristics, but 

 it is altogether a more delicate and slender species. 



Y 



\ 



\ 



a. Proximal portion. Enlargement of 



part of PL XLIX, fig. 3 a. 



b. Distal thecee, showing " acutus " ap- 



pearance in some of the thecse. 

 Ibid, 

 c and d. Various appearances presented 

 by the thecse. Ibid. 



