488 



MISS G. L. ELLES ON THE GRAPTOLITE [Aug. 1 898, 



(6) Tetragrapttjs cefcifee (Hall). 



1858. GraptolWms erucifer, Hall, Geol. Surv. Canada Rep. 1857, p. 125. 

 1865. Graptolithtis erucifer, Hall, ' Grapt. of the Quebec Group,' Geol. Surv. 

 Canada, dec. 2, p. 92 & pi, v, fig. 10. 



1868. Tetragrapsus erucifer, Nich. Quart. Journ. Geol. Soc. vol. xxiv, p. 144. 



A specimen in Mr. Postlethwaite's collection is the only one 

 known to me, therefore it would seem to be rare in the Skiddaw 

 Slates. This one 



Pig. 12. — Tetragraptus erucifer {coll. 

 Postlethwaite). 



agrees very well with 

 Hall's description. 



The general form is 

 like T. quadribrachi- 

 atus (Hall), but the 

 stipes widen very 

 much more rapidly 

 and are much stouter ; 

 and the disc is smaller 

 and more oblong than 

 it is in Tetragraptus 

 Headi (Hall). 



The stipes widen 

 rapidly from their 

 origin, and at the 

 same time are turned 

 over on to their sides 

 so as to reveal 'their 

 thecae, though all de- 

 tails are obscure. 



The maximum 

 width observed in any 

 stipe is fully i inch 

 (4-2 mm.) ; the great- 

 est length is 3^ inches 

 (82-4 mm.). 



The disc is small, [Nat. size.] 



quadrangular, and ob- 

 long, the greatest length being | inch (6*3 mm.), the greatest width 

 \ inch (4-2 mm.), and there is a very slight ' alation ' up the stipes. 



All details of the thecae are obscure. There seem to be twenty- 

 two apertures in the space of an inch (eight to nine in 10 mm.), 

 and these are situated obliquely with regard to the general direction 

 of the stipe. 



Occurrence. — On this slab there are also specimens of Azygo- 

 graptus suecicus, Moberg. The species also occurs with Tetragraptus 

 quadrihrachiatus (Hall). 



Locality. — Barf, near Keswick. 



(rt) Tetrageaptus Bigsbti (Hall). 



1853. Didymograpsus caduceus, Salt, (pars), Quart. Jouni. Geol. Soc. vol. ix, p. 87, 

 fig. 1 a. 



1858. FJiyllograptus similis. Hall, Geol. Surv. Canada Rep. 1857, p. 140. 



1863. Didymograpsus caduceus, Salt. ? Quart. Journ. Geol. Soc. vol. xix, p. 137, 

 fig.l3 6(?). 



