PLATE IV. 



Fig. Page. 



1. Promojjolseaster elizsn, 11. sp. ; photograph of apical sui'face, x 2. — Upper 



Ordovician (Ashgillian) ; Thraive Glen, Ayrshire. Mrs. G-ray's 

 Collection, no. D. 215. . 93. 



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



no. D. 216 c. 95. 



3. • Ditto; wash drawing of ossicles in the right of a groove, including the 



mouth-region, X 30 (approx.). — Ibid. Mrs. Gray's Collection, 

 no. D. 51. 95. 



4. Ditto j photograph of apical surface, X 2. — Ibid. Mrs. Gray's Collection, 



no. D. 104 c. 93. 



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



no. D. 32 c. 95. 



6. Palasterina ])vimseca, Forbes; photograph of extremity of one arm, nat. 



size. — Upper Silurian (Lower Ludlow) ; Leintwardine, Hereford- 

 shire. British Museum (Nat. Hist.), no. 40301. 



