704 SILURIAN TRILOBITES, 



Thorax. — Possesses nine segments, nearly square, greatest width 

 equal to its length. Axis prominent, wider than the pleural lobes; 

 rings faintly nodular at ends, dorsally each beai'ing two pro- 

 minent tubercles. Axial furrows distinct. Lateral lobes narrow; 

 pleural ridges and sutures very distinct, each pleural ridge bearing- 

 two very prominent tubercles, one at the fulcrum and the other 

 near the axial furrow; at least seven pairs of pleur:e bear acicular 

 spines, those on the third pair (none \isible on the first and 

 second pairs) are short, and at right angles with the axis, each 

 succeeding pair have an increasing backward flexion till the last 

 pair are parallel with the axis, they also increase in length pos- 

 teriorly; the fifth, sixth and seventh pairs are subfalcate, the 

 eighth and ninth pairs in some specimens show indications of 

 having stood upright. 



Pygidium. — Very small, widely triangular, distinctly tubercled. 

 Axis very prominent, consists of one ring and small terminal 

 piece; both bear a pair of small tubercles. Lateral lobes divided 

 into two pleurae by the pleural ridges extending from the ends of 

 the axis ring; these ridges are bituberculate; the border bears 

 eight acicular spines of nearly uniform length, four intermediate 

 and one on each side of the principal pair. Ajcial furrows distinct. 



Ohs. — This species was briefly described by Mr. F. Ratte,* and 

 determined by him to be near 0. Dormitzeri, but he pointed out 

 that it did not exactly agree with that or any other species known 

 to him. He noticed the small proportionate length of the tail to 

 the whole body, and the rounded contour of the free cheeks, 

 and with these observations we agree. In his description he 

 apparently fell into an error in assigning an ample genal lobe or 

 ti'iangular area, which we find to be very small, also in locating the 

 eyes much more forwai'd than they are in allied species. In this 

 latter feature it agrees with the 0. Leoahardi type in having the 

 eyes near the posterior border of the cephalon. It is, however, 

 separated from 0. Leonk'irdi and its congeners by possessing no 

 triangular areas on the glabella, in its more rounded and expanded 



* Proc. Linn. Soc. N.S. Wales, 1887, ii. (2), Pt. 2, p. 96, t. 2, f. 1, 1 bis. 



