PLATE XVII. 



LOWEST SILURIAN (ARENIG GROUP). 



Figs. 1 — 7. Ogygia Selwynii, Salter. 



1. „ „ Restored figure (not quite correct in proportions^ the 



glabella should be broader), chiefly from specimens 

 in the Museum of Practical Geology. 



2. ,, „ Glabella. (Mr. Lightbody's cabinet.) White Grit 



Mine, Shelve. 



3. „ ,, Compressed. Prom Llanfaelrhys, Aberdaron, South 



Carnarvonshire. (Miis. Pract. Geology.) 



4. ,, „ Large caudal shield, White Grit Mine. (Mus. Pract. 



Geology.) 



5. 6. „ ,, Thorax-joint and caudal shield. Same locaUty and 



cabinet. 



7. ,, „ Labrum. Same locality. (Mr. Lightbody's cabinet.) 

 Pigs. 8 — 10. Ogygia peltata, Salter, Prom Whitesand Bay, St. David's, Pem- 

 brokeshire. 



8. „ ,, A figure partly restored, and made too narrow in the 



axis, and the eye wrongly placed. Please to correct 

 this by fig. 10. 



9. 10. „ „ Parts of one fine specimen, pressed by cleavage-action 



into a shorter form than ordinary. (Cabinet of J. 

 E. Lee, Esq., Caerleon.) Pig. 9 should show faint 

 traces of the intermediate furrows of the tail-ribs ; and 

 fig. 10 shows the labrum broken at the tip, so as to 

 look like an Asaphus. It is, however, incomplete, 

 and must have been pointed, as in Ogygia. 



TREMAUOC rocks (uppermost CAMBRIAIS). 



Figs. 11 — 13. Ogygia scutatrix,^kVVY.K. Fig. 11, the specimen originally found at 



Garth, in Upper Tremadoc. Fig. 13, labrum, im- 

 perfect, from Portniadoc. (Mus. Pract. Geology.) 

 Fig. 12, tail from West of Penmorfa, Lower Tre- 

 madoc. (Mr. Ash's cabinet.) 



