Vol. 54.] 



PAUNA OF THE SKIDDAW SLATES. 



523 



slii]) Beck ; coll. Brit. 

 Mus. {Nat. Hist.). 



details of structure beyond external form ; the great length of the 

 spiniform appendages in proportion to the width of the rhabdosoma 

 is, however, highly characteristic. 



jS"icholson's type is in the British Museum (Nat. Hist.), and so 

 are all the other specimens known to me. The specimen that seems 

 to be the reverse of Nicholson's type appears to me to show more 

 than the figured side. 



None of the specimens exceed | inch 

 (6*3 mm.) in length, exclusive of the long Fig. 33. — Glossograptus 

 distal prolongation of the virgula. The armatus, from Tliorn- 

 general form of the rhabdosoma resembles 

 an elongated oval ; its maximum width is 

 jL inch (1-58 mm.). 



The spines are stout, the}^ are fully 

 -^^ inch (2'5 mm.) long, and are slightly 

 refiexed in every case except two near 

 the distal end, which are directed out-- 

 wards and upwards. Some appear to be 

 in pairs, but whether this is really the 

 case, or the result of a process of exfolia- 

 tion during preservation, I am not pre- 

 pared to say, though I incline to the 

 former view. 



The thecse seem to be more closely 

 set than Nicholson believed ; he reckons 

 twelve to the inch (five in 10 mm.), but 

 there are certainly six and probably seven 

 thec« on each side in some specimens, 

 and no specimen much exceeds | inch in 

 length (nine to eleven in 10 mm.). 

 Every theca seems to have been furnished with a spine. 



The species seems to be most closely related to Glossograptus 

 ciliatiis, Emm., from which it differs (1) in its smaller size ; (2) 

 in the greater length of the spines. 



Occurrence. — EUergill Beds = Upper Skiddaw Slates. 



Locality. — Thornship Beck, 



[X5.] 



Genus Trigonograptus, Nich. 



(a) Tkigofogeaptus ektsifoemis (Hall). (Fig. 34, p. 524.) 



1865. BetioUfes ensiformis, Hall, ' Grapt. of the Quebec Group,' Geol. Surv. 

 Canada, dec. 2, p. 114 & pi. xiv, figs. 1-5. 



1875. Trigonograptus ensiformis, Hopk. & Lapw. Quart. Journ. Geol. Soc. 

 vol. xxxi, p. 659 & pi. xxxiv, figs. 8 a-c. 



1890. Trigonograptus ensiformis, H. 0. Nich. Geol. Mag. dec. 3, vol. vii pp 340- 

 341, figs. 1 & 2. ' -^ ^' 



There are two specimens in the Woodwardian Museum which 

 seem to be referable to this species, and I have also seen one in 

 Prof. Nicholson's collection. 



According to Hall, the species has a maximum length of 2| inches 



