PLATE XI. 



Fig. Page. 



1 . Gnemidactis girvanensis (Schuchert) ; photograph of apical surface, 



X 2. — Upper Ordovician (Ashgillian) ; Thraive Glen, Ayrshire. 

 Mrs. Gray's Collection, no. D. 216 . . . .159 



2. Ditto ; photograph of oral surface, X 2. — Ibid. Mrs. Gray's Collection, 



no. D. 24 c . . . . .159 



3. Salteraster asperrimus (Salter) ; photograph of the apical surface, 



X 2. — Upper Ordovician (Caradocian) ; Quakers' Burial Ground, 

 Welshpool. Museum of Practical Geology, Jermyn Street, 

 no. 7435 . . . . . .150 



4. Photograph of the counterpart of the same specimen, x 2 . .150 



5. Salteraster (?) imbricatus (Salter) ; photograph of the apical surface, 



X 4. — Upper Ordovician (Caradocian) ; Llanfyllin, Montgomery- 

 shire. Museum of Practical Geology, Jermyn Street, no. 28364 . 152 



6. Salteraster (?) coronella (Salter) ; photograph of the apical surface, X 4. 



— Lower Silurian (Upper Llandovery) ; Gun wick Mill, near 

 Africk. Museum of Practical Geology, Jermyn Street, no. 7402 . 153 



7. Urasterella pulchella, Billings ; photograph of the mouth-region in oral 



aspect, x 10. — Middle Ordovician (Trenton) ; Ottawa, Canada. 

 Victoria Memorial Museum, Ottawa, no. 1397. The photograph 

 was sent to me by Dr. Hudson . . . .135 



8. Ditto ; photograph of the adambulacralia of the same species turned 



slightly on one side (after Hudson) x 10 . . 134 



