PLATE XVIII. 



Athyris (Cleiothyris) Royssii, Leveille, sp. (Page 148.) 

 Fig. 



1. Dorsal view of the cast of a young specimen, showing the central septum and 



the muscle-scars, X 3. Croyde. Museum of Practical Geology. 



2. Dorsal view of a similar specimen, showing the spire, X 3. 2 a, posterior 



view, showing the opening of the visceral canal, X 3. Croyde. Museum 

 of Practical Geology. 



3. Mould of another young specimen, showing the ornament, X 3. (This figure 



is drawn out of the perpendicular.) Poleshill. Porter Collection. 



4. Mould of a large distorted specimen, showing the fold and the ornament, 



which becomes closer and more spiniferous near the margins, X 2. 

 Pouch Bridge. Barnstaple Athenaeum. 



5. Distorted mould of another large specimen, with unusually numerous strias, 



X 2. Pilton. Porter Collection. 



Species Indeter. 



6. Cast of a ventral valve, showing muscular marks and signs of probable ribs, 



X 2. Poleshill. Porter Collection. 



Spirifera microgemma, Phillips. (Page 151.) 



7. Cast taken from the mould of a valve, showing ornament, but distorted in 



the region of the sinus, X 2. 7 a. Portion, X 5. Pilton. Porter Collec- 

 tion. 



8. A distorted dorsal valve, showing the fold, X f. Top Orchard. Barnstaple 



Athenaeum. 



Spirifera Verneuilii, Murchison. (Page 152.) 



9. A crushed individual, showing the hinge, X f. Pilton. Porter Collection. 



10. Portion of the cast of a specimen of the variety Sp. Barumensis, showing the 



spires. 



11. Portion of the surface of a large specimen, showing the minor longitudinal 



ornament, X 10. Ashford Strand. Barnstaple Athenaeum. 



12. Portion of another specimen, in which the transverse ornament is strong and 



the minor longitudinal ornament invisible, X 10. Ashford Strand. 

 Barnstaple Athenaeum. 



13. Ventral valve, seen from within, X f. 13 a, portion of surface, X 15, 



showing the arching lines of pores. Snapper Quarry. My Collection. 



