PLATE XXI. 



SILURIAN SPECIES. 



Fig. 



1 — 6. Rhynchonella Stricklandi, Sow. 1, \ a. After the original figure, ' Sil. Syst.,' pi. xiii, fig. 19. 



"Wenlock limestone ; Longhope. Mus. Geol. See. 2 — 2 h. A large 

 specimen from Wenlock shale ; Gaer-y-coed, Usk. Mus. Geol 

 Survey. 3, 4, 5. Three specimens from Wenlock limestone, Malvern. 

 6. A very fine internal cast of ventral valve, enlarged ; showing the 

 muscular and vascular impressions. (The ribs have not been 

 marked, in order to show the vascular markings the better.) 

 Wenlock limestone ; Tucking Mill, Usk. Mus. Geol. Survey. 



7 — 11c, and 12? Rhynchonella cuneata, Dalman. 7, 8, 9. Different specimens from the Wenlock 

 limestone of Dudley. 10 a. Beak enlarged, to show foramen and 

 deltidium. 11. A young example; a, b, c, enlarged. 11 c. Beak 

 very much magnified, to show the foramen and deltidium. 12. A 

 cast which has been referred to Rh. cuneata, from Mulloch Hill. 

 Ayrshire ; but this identification is uncertain. 

 13. Rhynchonella sexcostata, M'Coy. After the original figure in the 'Synops. Sil. Foss. Ireland,' 



pi. iii, fig. 30. Lettershambally, Leenane, County Galway. Sir 

 R. Griffith's Museum. The value of this species is uncertain, no 

 complete example having been found ; and it is here given simply 

 for sake of reference. 



14 — 20. „ borealis, Schloth. Figs. 14, 15, and 18. Three large typical specimens from the 



Wenlock limestone ; Longhope. Mus. Geol. Survey. 16,17. Two 

 varieties from Dudley. 19,20. A variety with a large number of 

 smaller ribs, termed Terebratula lacunosa in ' Silurian System,' 

 pi. xii, fig. 10. Wenlock Edge. 



21 — 23. „ ,, viLT. diodonta,D9\. Fig. 21, copied from Sowerby's figures of Terebratula 



bidentata, 'Sil. Syst.,' pi. xii, fig. 13a; and 'Siluria,' 2nd ed., 

 pi. xxii, fig. 5, where it is designated Rhynchonella borealis, var. 

 diodonta. Wenlock limestone ; Dudley. 22. Also from Dudley. 

 23. A small specimen from the Wenlock limestone of Falfield, 

 showing the scaly concentric ridges described by d'Eichwald. 



24—27. „ „ Variety. Fig. 24, from Wenlock Edge. Mus. Geol. Survey. 25 — 27. 



From Dvidley ; showing how variable is the number of the ribs ou 

 the fold and in the sinus. 



28. ,, Stricklandi {Terebratula crispata, Sow.). After the original figure, 'Sil. Syst.,' 



pi. xii, fig. 11. Mus. Geol. Soc. 



