PLATE 18. 

 Palaeodiscus feroz Salter. Page 250. 



Fig. 1. Lower Ludlow, Silurian, near Ludlow, England. British Mus. Coll., E 1,255. X 3.7. An external sandstone 



mold of the ventral side. Ambulacra relatively broad ventrally; there are ambulacral pores ventrally as usual in 



Echini. Interambulacral plates irregular, faint in definition; impression of spines; and lantern in place in which 



latter can be discerned the impressions of braces and epiphyses. 

 Fig. 2. Lower Ludlow, Silurian, Church Hill, Leintwardine, England. British Museum Coll., E 1,252. X 3.7. An 



external sandstone mold of the ventral side. Ambulacral plates only on the peristome. Ambulacral plates in the 



corona have pore-pairs ventrally. 

 Fig. 3. Same specimen. Mold of the exterior. -X 15. Ambulacral pores are in about the middle of each plate, fine 



spines on the interambulacral plate. 

 Fig. 4. Same specimen, impression of the interior. X 15. Shows ambulacral pores in the median line of each plate and 



a lateral extension of ambulacral plates beneath the interambulacral areas on either side. 

 Fig. 5. After Sollas,. 1899, fig. 7, p. 702, enlarged. Dorsal view, showing compasses, braces, and epiphysea. Original 



in Oxford University Museum. 



Echinocystites pomum Wyville Thomson. Page 252. 



Fig. 6. Lower Ludlow, Silurian, Leintwardine, near Ludlow (after Gregory, 1897, Plate 7, fig. 4). X 0.9. Shows am- 

 bulacra and interambulacra with spines and a madreporite. 



Fig. 7. After Gregory, 1897, fig. 1, p. 125. Ambulacral plates of a half-area, much enlarged. 

 Fig. 8. After Gregory, 1897, fig. 2, p. 125. Pyramid "seen from behind," enlarged. 



Figs. 1-4 drawn from nature, and figs. 5, 6 copied by J. Henry Blake; figs. 7, 8 copied by W. M. Barrows. 



