Nileus armadillo Dalman 



8 Exfoliated cephalon (a portion of the very thick crust is still 



preserved at the right, above and below the eye) with dis- 

 tinctly pitted interior cast of eye tubercle. (From Schmidt) 

 Ordovician : Expansusstufe B 2 b, Paulowsk, Gouvern. Peters- 

 burg, Russia. 



Ceratopyge forficula Sars 



9 Partly exfoliated cranidium with interior cast of eye tubercle. 



(From Moberg & Segerberg) 

 Ordovician : Ceratopyge beds, Ottenby, Sweden. 



Hysterolenus tornquisti Moberg 

 10 Cranidium with well-developed median eye tubercle. (From 

 Moberg & Segerberg) 

 Ordovician : Ceratopyge beds, Fogelsang, Sweden. 



Niobe insignis Linnarsson 

 ii Partly exfoliated cranidium with distinct interior cast of 

 median eye tubercle. (From Moberg & Segerberg) 

 Ordovician : Ceratopyge beds. Ottenby, Sweden. 



Barrandia crassa Barrande 



12 Partly exfoliated cephalon, showing distinct interior cast of 



median eye tubercle. (From Barrande) 

 Ordovician : d x . St Benigna, Bohemia. 



Aeglina umbonata 



13 Exfoliated glabella with interior cast of median eye tubercle. 



(From Moberg) 

 Ordovician: Orthoceras limestone. Fogelsang, Sweden. 



Illaenus oriens Moberg & Segerberg 



14 Dorsal view of cranidium with median eye tubercle and outline 



of profile view, to show apical position of tubercle. (From 

 Moberg & Segerberg) 

 Ordovician: Ceratopyge beds. Ottenby, Sweden. 



Bronteus haidingeri Barrande 



15 Cranidium with median eye tubercle. (From Barrande) 

 Silurian: E. Dlauha Hora, Bohemia. 



