Victorian FossiL^, Part XII. ^15 



terior segment. Occasional faint tubercles and striae are seen 

 both on the lateral lobes and axis. 



Dimensions. — Head-shield (small specimen) ; length, 2.5 mm. ; 

 width, 2.75 mm. Tail-shield : Length, about 4.5 mm. ; width. 

 5 mm. 



Affinities. — ^This form is closely related to Agnostus j^i'^i- 

 formis, Linne, sp., and is therefore embraced in the section 

 Longifrontes of TWlberg.^ In general shape and structure it 

 resembles A. iJisiformis (typica),^ especially in the form of the 

 cephalon ; but in the breadth of the pygidium it is most like 

 the variety of that species named otiet^ux by Belt. 3 



Robt. Etheridge in his " Fossils of the British Islands,''"* in- 

 cludes A. piriformis under A. prince ps, Salter, together with 

 Belt's variety obesus, and gives the horizons as Lingula Flags 

 and Tl-emadoc. On the other hand Lake, in his later and more 

 critical work, 5 states that Salter's A. j'^^incejis was founded on 

 specimens of three distinct species — viz., A. trisectus, Salter, 

 A. pisiformis, L. sp., and A. rudis, Salter. To revert to Lake's 

 determinations of A. j^i'^iformis var. obesus. and its horizon, 

 that author gives the latter as Lower Lingula. Flags, but adds, 

 '' In some cases the horizon is given as Menevian, in others 

 Upper Lingula Flags, but these determinations may be 

 doubted."^ It will therefore be seen that the nearest allied form 

 to our species, as occurring in Britain, is typical of the Upper 

 Cambrian or Olenus Fauna. 



Another species with which comparison may be made is 

 Agnostus punctuosus, Angelin,^ a species found in the Para- 

 doxides fauna (Menevian). This form differs, however, in the 

 closely tuberculated surface of the head and tail, and also in the 

 less tumid cheeks and pygidial lobes. 



1 See p. Lake. Mon. Brit. Cambrian Trilobites, Pal. Soc, 1906, pp. 2, 3. 



2 £a'a(.s pi>(yormM, L. sp., Hisinger, 18a7, I.eth. Suee., p. 19, pi. iv., fij;. 5 (fissured 

 head downwards). AgnoatUH pimfnrmis, L. sp., Angelin, 1852, Pal. Scand., p. 7, pi. vi., 

 fig. 7. Lake, Mon. Brit. Camb. Trilobites, 1906, p. 9, pi. i., fig. 12. 



3 Belt. Geol. Mag., vol. iv., 1867, p. 29.=i, pi. xii., figs. \n-d. Lake, loc. cit. p. 9. pi. i.i 

 figs. 13, 14. 



4 Vol. i.. Palaeozoic, 1888, p. 41). 



5 Loc. cit., p. 12. 



6 Loc. cit., p. 10. 



7 Angelin, Pal. Scand., 1852, p. 8, pi. vi,, fig. U. Lake, loc. cit., p. 4, pi. i., figs. 4-6. 



