BY R. ETHERTDGE, JUNR., A'NTD JOHN" MITCHELL. (S61 



eye-section appears to be subelliptical, but this arises from lateral 

 compi'ession. Nor does there appear to loe any constant ratio, in 

 most specimens, between the entire length of the body and that 

 of either the cephalon or pygidium, but, in a few mature indi- 

 viduals, the length of the thorax and pygidium were found to be 

 equal, yet in many cases the former exceeded the latter in length. 

 It should be noted, too, that the whole of the submucronate ex- 

 tension of the pygidial axis is seldom preserved, and, therefore, 

 the actual length of the pygidium rarely determinable. Although 

 nearly all the pygidia, which are very many, show only ten 

 pleural segments in each side-lobe, two or three have come under 

 notice which faintly indicate an additional one very intimately 

 fused to the submucronate tail terminal. Hence it may be that, 

 in this species, the normal number of segments in the pleural 

 lobes of the tail is eleven instead of ten, as indicated in our 

 description. 



E. konghsaensis^ Reid,* from the Lower Palaeozoic rocks of 

 Burma, presents many points in common with E. inifchflli, par- 

 ticularly in the form and position of the cephalic axial tubercles; 

 the two species, however, are distinct. E. mitchelli is the com- 

 monest trilobite in the Lower Trilobite Bed of the Bowning 

 (Yass and Hume) Series. 



hoc. and Hor. — Lower Trilobite Bed, Bowning Series, Parish 

 Bowning, County Harden, N. 8. Wales; Hatton's Corner, Yass 

 River, Parish Yass, County Harden, N. S. Wales; Silverdale 

 Limestone and Jones' or Derrengullen Creeks, Parish Bowning, 

 County Harden, and Parish Derrengullen, County Murray ; 

 Warroo Creek, Parish Warroo, County Murray (J. M.); shale and 

 limestone bands west of contorted shales, Boambola Crossing, 

 Murrumbidgee River (A. J. 8hearsby; Coll. Aust Mus.); Hatton's 

 Corner, shale below the limestone, Hardy's or Limestone Creek, 

 Parish Derrengullen, County King (Coll. Aust. Museum; pre- 

 sented by A. J. Shearsby). 



* Reid, Lower Pal. Foss, N. 8han States, Burma (Pal. Ind., N.S. ii., 

 Mem.3), 1906, PI. vii., fig.21. 



