176 Observations on Trilobites. 



IsoTELusgigas.* Plate XII. fig 1. PI. XIII. fig. 1. 



Head representing a spherical triangle, surface punctate, 

 convex descending from between the eyes to the anterior bor- 

 der, which has a narrow raised rim : posterior extremity con- 

 cave and corresponding to the articulation of the abdomen* 

 Eyes elevated, prominent, sub-pedunculated ; cornea eblong, 

 lunated, highly polished. Abdomen with eight distinct articu- 

 lations, the middle lobe double the size of the lateral one : 

 these latter are continuous with the middle lobe, have a deep 

 furrow impressed on their upper surfaces, which becomes 

 gradually effaced towards their narrow free extremities. These 



Genus Ogygia. 



Body much depressed into an oblong - ellipsis, not contractile into a 



sphere. 

 Buckler bordered, a slight longitudinal furrow arising- from its anterior 



extremity. Posterior angles elongated into points. 

 Longitudinal lobes not very prominent. 

 Abdomen with 8 articulations. 



Eyes not prominent nor reticulated ; no other protuberances on the 

 buckler. 



2 species. 

 Genus Paradoxides. 



Body depressed, not contractile. 



Flanks larger than the middle lobe. 



Buckler nearly semi-circular ; three transverse furrows on the middle 



lobe ; no ej^e-shaped tubercles. 

 Abdomen with 12 articulations. 



Articulations of the lateral lobes extended more or less beyond the 

 membrane which sustains them. 

 5 species. 

 Genus Agnostus. 



Body elipsoid, semi-cylindrical. 



Buckler and flanks bordered, with the edges raised. 



Middle lobe with two transverse divisions each composed of a single 



piece. 

 Two glanduiar tubercles on the anterior part of the body. 

 1 species. 



