CHEIRURUS. 9 



Margins spinous at the sides, inclining rapidly to each other, but turning before 

 they meet to form two spines at the posterior end. 



Size of head. — 23 mm. in length, 38 mm. in width (excluding spine), and 8 mm. 

 in depth. 



Localities. — From Lummaton there are nine specimens of the head in my 

 collection, one in the Bristol Museum, two in the Lee Collection in the British 

 Museum, three or four in the Torquay Museum, and three in the Woodwardian 

 Museum, in which also there is a poor but unique specimen of the tail and a small 

 hypostome. There are also two examples of the hypostome in my collection. 

 From Wolborough there is a single head in Mr. Vicary's Collection. 



Remarks. — The specimens at our disposal have for the most part lost both 

 their outer surface and their free cheeks, and in no case has the eye been fully 

 preserved, though its loss seems generally due to accidental fracture. Never- 

 theless, these fossils are very distinctive, and present much detail, and, judging 

 from them, this species, which has been admirably and minutely described by 

 Salter, is subject to very little variability, and therefore minute distinctions must 

 be considered of importance. Thus the profile of the head and the proportions of 

 the frontal lobe seem always to remain much the same, and to give slight but 

 constant specific characters. The single known specimen of the tail is in a far 

 less satisfactory condition than could be desired. At first sight it appears 

 perfectly distinct from that of any kindred species, but the margin is imperfect, 

 and the traces of lateral spines have been obliterated. Nevertheless, even thus 

 it affords important help. 



There appears to exist much confusion with regard to the naming of this species. 



Miinster, in his ' Beitrage,' Pt. 3, pi. v, figures three species of Gheirurus 

 under the names of Calymene SternbergiiJ G. propinqua, 2 and G. articulata. 3 With 

 the first of these Phillips identified our Devonshire fossil. This identification 

 Salter rejected, because in that species the furrows vanish in the centre of the 

 glabella ; but he in turn identified it with G. articulata, at the same time remarking 

 that Minister's figures are evidently inaccurate, and that if accurate this identifi- 

 cation could not stand. Neither in the ' Decades ' 4 nor in his Monograph 4 does 

 he give any indirect reason for supposing it to belong to this species. The only 

 argument in favour of it appears to be that Barrande 5 states that he has examined 

 the originals of Minister's figures and finds that the G. Stembergii and propinqua 

 of that author are probably one species, and approach his own Gh. Haivlei, while 

 G. articulata is distinct, and belongs to the group of Ch. gibbus ; and that 

 Sandberger 6 identifies Gh. gibbus with Phillips's figure. We shall, however, show 



1 Loc. cit., p. 37, pi. v, fig. 5. 2 Loc. cit., p. 38, pi. v, fig. 6. s Loc. cit., p. 38, pi. v, fig. 7. 

 4 See above, p. 8 (synonymy). 5 Barr., ' Syst. Sil.,' vol. i, p. 754. 



6 Sandb., ' Verst. Nassau,' p. 19, pi. ii, fig. 2. 



