TRILOBITA. 



529 



sutures nearly parallel, cutting the head-shield separately ; the eyes 

 large. The body is very long (fig. 385, a); the thorax has from 

 twelve to twenty segments, with grooved pleurae ; the pygidium 

 being usually small and of few segments. The family is essentially 

 characteristic of the Cambrian deposits, ranging through all the 

 divisions of this formation. 



The principal genus of this group is Paradox ides itself (fig. 385, a, 

 and fig. 386), with its long and trilobed body, sometimes reaching 

 a length of two feet or more. The thorax in this genus is greatly 



Fig. 385. — Paradoxidce and Conocephalidc?. a, Paradoxides Bohemicus, reduced in size; b, 

 Ellipsocephalus Hojft; c, Sao hirsute; d, Conocoryphe Sultzeri — (all the above, together with 

 fig. £-, are from the Upper Cambrian or "Primordial Zone" of Bohemia); e, Head-shield of 

 Dikellocephalus Celticus, from the Lingula Flags of Wales; /, Head -shield of Conocoryphe 

 Mattheivi, from the Upper Cambrian (Acadian Group) of New Brunswick ; g, Agnostus rex, 

 Bohemia; h, Tail-shield of Dikellocephalus Minnesotensis, from the Upper Cambrian (Potsdam 

 Sandstone) of Minnesota. (After Barrande, Dawson, Salter, and Dale Owen.) 



elongated, and consists of sixteen or twenty rings, while the axis of 

 the pygidium often contains two segments only. The eyes are 

 long, reniform, and smooth. The genus is characteristic of, and 

 confined to, the Cambrian period. Plutonia and Anopolenus, with 

 a similar geological range, are closely related to Paradoxides ; but 

 the former of these two genera has a narrow glabella and a tuber- 

 culated surface, while the latter has the last two pleurae of the thorax 

 dilated and bent backwards, and the pygidium has wide lateral lobes. 

 The genus Olenelhis resembles Paradoxides in most respects, but 

 vol. 1. 2 L 



