G98 SILURIAN TRILOBITES, 



spines long and acicular, anterior ones short and lanceolate and 

 serrated, all much deilected. Axial furrows faint. 



Pygidium. — Small, about four times as wide as long, strongly 

 tubercular; the anterior margin straight between the fulcra, thence 

 gently turned backwards. Axis prominent, consisting of one highly 

 arched anterior ring and a terminal piece which is ridged and 

 circumfurrowed, and centrally depressed. The lateral lobes are 

 divided into two pairs of pleurse by one pair of pleural ridges, ex- 

 tending from the axis ring; they are flat, tuberculate and punctate, 

 border much thicker and internally bounded by a distinct furrow. 

 Tail spines fourteen, acicular, four intermediate and four on each 

 side of the axial pleural spines, the latter diminishing rapidly in 

 length from the axial pair outwards, so that the first and second 

 pairs are very short. 



Ohs. — The striking features of this species are : — (1) The great 

 proportionate width, particularly of the cephalon; (2) the deflected 

 spines and short, jutting, obtuse hornlike genal spines; (3) the 

 very small eyes ; (4) the absence of an occipital tubercle ; (5) the 

 great width between the eyes and their nearness to the posterior 

 margin of the cephalon; and (6) the excessive tumidity of the 

 cephalon as a whole. 



Whilst resembling 0. ovata, Burmeister,* the generic type, in 

 the great proportionate breadth of the body to its length, our 

 form departs very markedly in possessing ten instead of eight 

 thoracic segments, in the very small pygidium, the increased 

 nvimber of spines around the margin of the latter, and in the 

 shorter and stouter genal spines. Similar characters separate it 

 from 0. elliptica, Burmeister.f From an allied American species, 

 0. crossota (Locke), Meek, J our species is separated by the size, 

 shape, and segmentation of the pygidium. In this species also 

 the facial suture extends even further laterally than in 0. hoio- 

 ningensis, and there is no occipital tubercle. 



* Organization of Trilobites, 1846, p. 62, t. 2, f. 11. 



t Lor. cit. p. 63, t. 1, f. 4. 



X Ohio Geol. Report, 1873, I. t. 14, f. 10, 10a. 



