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Genus Second. ASAPHUS. 



Body broad and rather flat. Middle lobe promi- 

 nent and very distinct. 



Flanks or lateral lobes each double the size of the 

 middle lobe. 



Submembranaceous expansions extending beyond the 

 lateral lobes. 



Buckler semicircular, with two reticulated eye- 

 shaped tubercles. 



Abdomen divided into 8 or 12 articulations. 



Genus Third. OGYGIA. 



Body much depressed into an oblong ellipsis not 

 contractile into a sphere. 



Buckler edged, a slight longitudinal furrow aris- 

 ing from its anterior extremity. Posterior angles 

 elongated into points. 



Without any tubercles except the eyes, which are 

 neither prominent nor reticulated. 



Longitudinal lobes slightly prominent. 



Abdomen with 8 articulations. 



Genus Fourth. PARADOXIDES. 



Body depressed not contractile. 



Flanks much broader than the middle lobe. 



Buckler nearly semicircular three transverse fur- 

 rows on the middle lobe. 



Eye-shaped tubercles none. 



Abdomen with 12 articulations. 



Arches of the lateral lobes, more or less prolonged 

 beyond the membrane which sustains them. 



