44 EXPLANATION OF THE PLATES. 
Fig. 6.—a, b,c. STROPHOMENA COMPRESSA, Sowerby, sp. 
Orthis, Sil. Syst., p. 638. Strophomena, Sil., fourth edition, pl. ix., fig. 16. 
a. Original. In yellow sandstone, from Harnage, S. E. of Shrewsbury. 
Mus. G. S. I. 
b. Original. Portion of surface of 6 a enlarged. 
ce. Internal cast. From Sil., fourth edition, Fossils, 15, p. 90. 
Luanpovery and Wentock.—Sil., fourth edition, p. 528. Upper Llan- 
dovery, Presteign; Marloes Bay ; Norbury ; Chirbury; Malverns ; also 
Bogmine, near Shelve, Shropshire. M. G.§%., vol. ili., pp. 861-2. 
Fic. 7.—a, b, c. LEPTHNA TRANSVERSALIS, Dalman. 
Silurian System, p. 629, pl. xiii., fig. 2. ZL. duplicata, ibid., p. 636, pl. xxii., 
fig. 2.0. transversalis, Sil., fourth edition, pl. ix., fig. 17; and pl. xx., 
fig. 17. 
a. Upper or dorsal view ; from Sil. Syst., pl. xiii., fig. 2. 
b. Lower or ventral valve ; from Sil. Syst., pl. xi., fig. 2. 
c. Internal cast ; from Sil. Syst., pl. xxii., fig. 2. 
Carapoc to Wentock.—Sil., fourth edition, p. 525. Caradoc. Glyn-ceiriog, 
Denbighshire ; Bala, &c. M. G.S., vol. i., p. 267. Upper Llandovery, 
Builth; N. of Llandovery ; Pen-y-lan ; Malverns; Longmynd; Norbury ; 
Chirbury. M. G. §., vol. iii., p. 361. Wenlock, Walsall, Woolhope, 
Ledbury, &c. Sil. Syst., p. 629. 
Fic. 8.—a, 6, ec. ORTHIS REVERSA, Salter. 
Silurian Fossils, Ireland, Addenda, p. 72, pl. v., fig. 2. 
a. Original. Internal cast of dorsal valve; Maume, Co. Galway. Mus. 
G8 
b, Original. Internal cast of ventral valve; Maume, Co. Galway. Mus. 
J : 
c. External surface of shell; var. Girvanensis, Davidson. From Brit. Sil. 
Brach., pl. xxix., fig. 18. 
Llandovery. Sil., fourth edition, p. 527. Lower Llandovery, Mandinam, 
Caermarthenshire; Mus. G. 8.1. ? Upper Llandovery, Girvan Water, 
Ayrshire; Mus. G. 8. I. Upper Llandovery, Llandovery ; Malverns ; 
Tortworth ; Chirbury; Norbury; Bogmine. M. G. S., vol. iii., p. 361. 
In Ireland it is not uncommon in (?) Upper Llandovery beds near Cong, 
Co. Galway. 
Fic. 9.—a, 6. MERISTELLA ANGUSTIFRONS, M‘Coy, sp. 
Hemithyris, Brit. Pal. Foss., p. 199, pl. 1 H., figs. 6-8. 
a. External surface of shell; from Brit. Sil. Brach., pl. x., fig. 22. 
b. Original. Impressions of the interior, showing various positions ; in 
greenish and ferruginous sandstone, Mulloch Hill, Ayrshire. Mus. G. 8. I. 
Llandovery, Sil., fourth edition, p. 525. “This characteristic species of 
the Lower Llandovery rocks, first described from the sandstones of 
Mullock, Ayrshire, has also been detected near Builth and in the lower 
beds at Llandovery. Sil., fourth edition, p. 209. In Scotland it occurs 
by millions in 4 greenish and rusty-coloured sandstone at Mullock Hill, 
