PLATE XVIII. 



a. Amphiura Prattii, Forbes, p. 156. Under surface, natural size; this speci- 

 men belongs to the British Museum. 

 i- „ ,, Portion of a ray, magnified four times. 



c. „ ,, Ditto of the base, magnified four times. 



f^- ,, ■ Lateral portion, magnified four times. 



Small specimen coiled up on a slab, 

 natural size. British Museum. 



a. Ophiurella Griesbachii, Wriglit. p. 154. Natural size, under surface ; this 



specimen belongs to Dr. 

 Wrio;lit's collection. 



^- ,, „ The same, magnified three and a 



half diameters. 



„ ,, _ Portion of a ray, showing spines, 



magnified six diameters. 

 n. Ophioderma tenuibraceiata, Forbes, p. 146. Under surface, natural size, on 



a slab of Middle Lias sand- 

 stone; this specimen belongs 

 to Dr. Wright's collection. 



b. „ „ Portion of a ray, magnified 



four times. 



c. ,, „ Terminal portion, magnified 



four times. 



