PLATE XVIII. 



SILURIAN SPECIES. 



Fig. 



1 — 3. Pentcmerus ohlongus, Sow. After Sowerby's original figures (' Sil. Syst.,' pi. xix, 



fig. 10). Upper Llandovery; Shropshire and Llan- 

 dovery. 



4,4a. „ Upper Llandovery; Hope Quarry, N.E. of Chirbury. 



Mus. Geol. Survey of London. 

 5. „ „ Internal cast of ventral valve, showing the median septum . 



Upper Llandovery, Norbury. Mus. Geol. Surv. 

 6 — ^1). „ „ Internal cast. Upper Llandovery ; Nash Scar, Presteign. 



Mus. Geol. Surv. 



' 7. „ „ Internal cast of ventral valve. Upper Llandovery ; the 



Hollies, Wrekin. Mus. Geol. Surv. 

 8. „ „ Ventral valve. Boocaun, Cong, County Galway, Ire- 



land. Sir R. Griffith's Collection. This is the 

 specimen referred to by Prof. M'Coy in his ' Synopsis 

 Sil. Foss., Ireland,' p. 38. 

 9- „ „ Internal cast, seen from the beaks, and showing the 



position of the septa and converging dental plates in 

 both valves. Upper Llandovery ; Craig-yr-Wyddou. 

 Mus. Geol. Surv., London. 



10. „ „ Small specimen. Llandovery rock ; Ardmillan, Ayrshire. 



Mr. D. J. Brown's Collection. 



11- „ „ Longitudinal section, showing the septa and dental 



plates. Cappacorcogue, Cong, County Galway. Sir 

 R. Griffith's Collection. 



12. „ „ {P. lavis, Sow.). A fragment {' Sil. Syst.,' pi. xix, fig. 9). 



Upper Llandovery ; Shropshire. 



