BY R. ETHERIDGE, JUXR., AND JOHN MITCHELL. 701 



acicular spines, except in the case of the first pair of pleural on 

 each lobe, which are very rudimentary; the spines of the third 

 pair equal the length of the thorax and tail together, and are 

 fleeted backwards at about -to", each succeeding pair increasing 

 in backward flection till those from the last pair are rectangular 

 to the thorax. 



Pygidium. — Widely triangular, rather flat, strongly granu- 

 lated; front mai'gin straight between the fulcra, thence backwards 

 at an angle of 45^ nearly. Axis short, consisting of one 

 very prominent ring and terminal piece, the latter clearly 

 separated from the former b}'' a furrow, and bearing a small 

 but distinct and persistent granule on each side, and is also 

 nearly circumfurrowed. From the ends of the axis ring- 

 extend a pair of pleural ridges obliquely and distinctly across 

 the lateral lobes, and are produced into the axial or pleural spines. 

 Side lobes divided into two lobes, one pair of pleural furrows 

 present, border bearing twelve to fourteen acicular spines, two 

 intermediate and four to five exterior to the axial pair ; the first 

 two on each side adjacent to the anterior face are rudimentary 

 and seldom visible when the tail is attached to the thorax ; the 

 pleural pair have a length equal to half the length of the thorax; 

 intermediate pair appear to be about two-thirds as long as the 

 axial pair ; all bear a row of granules. 



Obs. — This species is one of those figured by the late Mr. Felix 

 Ratte,* and placed by him near 0. Leonhardi, Barr., although 

 he was careful to point out that it did not strictly accord with 

 that Trilobite. 



From the preceding form, 0. hoivningensis, nobis, it may be at 

 once distinguished by possessing a segment less in the thorax, by 

 the presence of frontal spines or serrations to the glabella proper, 

 and so far as we are able to discern, by the thoracic pleurae being 

 unispinate only ; furthermore, it is a more slender species. The 

 genal spines are very different, as are also the pygidium and other 

 parts. 



* Proc. Linn. Soc. N.S. Wales, 1SS7, ii- (2), Pt. 2, p. 99, PI. ii. figs. 2-4, 



