PLATE XIII. 



SILURIAN SPECIES. 



Fig. 



1 — 3 a. Meristella 1 crassa, Sow. sp. 1. Exterior of dorsal valve. Lower Llandovery ; Cefn-Rhyddan. 



2. Internal casts of ventral valve. 2 a. Mould in gutta-percha from the 

 same. Same Locality as fig. 1. (Murchison's original specimen.) Mus. 

 Geol. Society. 3. Internal cast of dorsal valve. 3 a. An enlarged fig. from 

 a mould in gutta-percha of the same cast. Mus. Geol. Soc. 



4 — 4 c. „ subundaf a (Hemithi/ris, M'Coy). After the original figures in 'Brit. Pal. Foss.,' 



pi. i H, figs. 9, &c. Fig. 4, enlarged ; 4 a, b, c, nat. size. (This shell is not 

 very unlike in shape to some flattened specimens of If. tumida.) Wood- 

 wardian Museum, Cambridge. 



5 — 5 a. Athyris ohovata, Sow. 5. Nat. size. 5 a. A considerably enlarged interior of the ventral 



valve, to show the muscular and vascular impressions. Lower Ludlow. 

 Collection of Dr. Holl. 



6 — G h. „ ? depressa, Sow. 6. Nat. size. 6 a, h. Enlarged figures from a young but perfect 



example. Woolhope limestone. Road between Alfric and Crew Hill, 

 Malvern. 



7_9. Meristella 1 furcata{Terehratula,^QW.). 7- Internal cast of ventral valve, nat. size. 7 a. The 

 same enlarged. 7 b. A gutta-percha mould from cast, also enlarged. South 

 of Bogmine, near Corndon Hill. This is the original specimen figured 

 in 'Sil. System' (pi. xxi, fig. 16). 8, 9. Other casts (after the original 

 figures) . 



10 — 1,3c. Retzia'i Barrandi, Dav. A series of specimens, showing modifications in shape; from the 

 Wenlock limestone of Dudley, Hay Head near Walsall, and Buildwas near 

 Wenlock. 12 a, and 13 a, b, c, d, are enlarged illustrations. 



14 — 22. Atrypn 1 Grayii, Dav. A series of modifications of this singular shell, from the Wenlock lime- 

 stone of Dudley, and Hay Head, near Walsall. Fig. 14 is the largest example 

 hitherto found. Figs. 14 a, 15 a, 16a, i,c, \7 b, 18a, 6, 19, 20, 21, and 

 22, are enlarged figures. 



23 — 30 a. „? hemisph(Erica (Atrypa, So\i/.). A variety of specimens. 23. Copy of the original 

 illustration in ' Sil. Syst.,' pi. xx, fig. 7. Upper Llandovery, May Hill. 

 24. Nat. size, and 24 a, b c, enlarged, from the Upper Landovery, Charfield 

 Green. Mus. Geol. Survey. 25. From the Upper Llandovery, Ardmillan, 

 Ayrshire. 26. Mullock Hill, Ayrshire. 27. Penkill, Ayrshire. 28. From 

 Ankerdine, in May Hill sandstone. 29. Internal cast of ventral valve, nat. 

 size, and 29 a, enlarged, from Penwhapple Glen, Ayrshire. 30 and 30 a. 

 Internal cast of dorsal valve. Mus. Geol. Survey. 



31—316. „ Scotica, M'Coy. After the figures in Brit. Pal. Foss., pi. in, fig. 10. Mullock; 

 Dalquoran ; Woodwardian Museum, Cambridge. 



