DICELLOGRAPTUS. 1 57 



There are good specimens in the collections of the Geological Survey of 

 Scotland, the Sedgwick Museum, and also in the private collections of Lapworth 

 and the Authors. 



Dicellograptus moffatensis, Carruthers. Plate XXT1T, figs. 1 <i—f. 



1858. Didymograpsus moffatensis, Carruthers, Proc. Roy. Soc. Eclin., vol. i, pt. 2, p. 469, fig. 3. 



1871. Dicellograpsus moffatensis, Hopldnson, Geol. Mag., vol. viii, p. 25, pi. i, figs. 4 a, 4&. 



1875. Dicellograptus moffatensis, Hopldnson and Lapworth, Quart. Journ. Geol. Soc, xxxi, p. G54, 



pi. xxxiv, fig. 3, pi. xxxv, fig. 5 a. 



1870. Dicellograptus moffatensis, Lapworth, Cat. West. Scott. Foss., pi. iv, fig. 84. 



1877. Dicellograptus moffatensis, Lapworth, Grapt. Co. Down, pi. vii, fig. 9. 



1895. Dicellograptus moffatensis, Elles, Quart. Journ. Geol. Soc, vol. liv, p. 516. 



Stipes robust, 8 cm. or more in length, straight or slightly curved, sub-pnrallel 

 for a short distance proximally, then diverging at large but varying angles ; 

 increasing abruptly in width at the proximal end and then more gradually 

 throughout ; frequently connected at their origin by a corneous membrane. 

 Thecse eleven to nine in 10 mm., overlapping one half to one third their length, 

 ventral wall strongly curved. Apertures introverted, opening within a wide 

 and rather shallow excavation which occupies about one third the width 

 of the stipe and one third to one quarter of the free part of the ventral wall. 

 Description . — The typical shape of the stipes is characteristic, but varies some- 

 what in different specimens. The stipes, however, always show a tendency to 

 sub-parallelism for the first cm. of their length, then either diverge continuously, 

 or curve slightly towards each other distally. The stipes measure less than *5 mm. 

 in width at their origin and increase abruptly until a breadth of 1 mm. is reached, 

 after which the increase is gradual, and a maximum of 1*5 mm. may be attained. 

 Fms. 99 a and b. -Dicellograptus Moffa- The corneous membrane is present in most speci- 

 tensis, Carr. mens, and may extend from the proximal end as 



far as the level of the fourth thecal aperture. As 

 Hopkinson has observed, when the stipes are joined 

 proximally by this membrane the axillary angle is 

 smaller than when they are not thus united, but 

 " , , .„ , i n we find that this is not invariably the case. 



a. Proximal end, with "web. On same ^ 



slab as pi. xxin, fig. i «. The sicula is rarely discernible, being often 



b. Proximal end, showing sicula. En- 



largement of part of PL xxin, concealed by the membrane, but when shown is seen 

 fig. i c. J 



to have a length of about 1 mm., and is narrow and 



tapering. The virgella and lateral spines of th. I 1 and th. I s are short but 



generally conspicuous. Th. 2 1 and th. 2 2 are also furnished with spines, but the 



remaining thecae arc devoid of ornament. 



