TRILOBITA. 



365 



these two genera has a narrow glabella and a tuberculated 

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

 dilated and bent backwards, and the pygidium has wide 

 lateral lobes. In Hydrocephalus, again, the glabella is im- 

 mensely inflated, with a median longitudinal groove ; and 

 the facial sutures cut the outer margins of the head-shield, 

 so that the free cheeks become much reduced in size, and 



Fig. Stl^Pmradoxidas and Conocephalidte. a, Paradoxides Boliemicus, reduced in size ; &, 

 EHipsucephalus Hoffi ; c, Sao lilrmta ; d, Conocoryphe Sultzeri (all the above, together with fig. 

 g, are from the Upper Cambrian or "Primordial Zone " of Bohemia) ; e, Head-shield of Dikel- 

 loceplialus Celticits, from the Lingula Flags of Wales ; /, Head-shield of Conocoryphe Matthewi, 

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

 Tail-shield of Dlkelloceplialus Minnesotensis, from the Upper Cambrian (Potsdam Sandstone) 

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



the genal spines are attached to the fixed cheeks. Eyes are 

 wanting, and there are only twelve body-rings. A more 

 important and widely distributed genus of this family is 

 Olenus (fig. 223), in which the general characters are very 

 similar to those of Paradoxides, but the glabella is contracted 

 in front so as to become conical, and its furrows are often 

 extended completely across it : there are only fourteen body- 

 rings ; and the pygidium is well developed. Parabolina 



