EXPLANATION OF THE PLATES. DAI 
CONCHIFERA. 
Fig. 7.—a 6. PALHZARCA SOCIALIS, Salter. 
From Mem. Geol. Surv., vol. iii., p. 344, pl. xi. A, fig. 13, 13 b. 
The form, as in fig. 7, a, is that of an Arca ; when distorted, as at 7 b, 
it resembles Modiola, and in such state is very likely to be mistaken for 
that or some other genus. 
Lower LianDEILo.—Ty-obry, Penrhyn, opposite Tremadoc, abundant. 
Fie, 8.—REpoNIA ANGLICA, Salter. 
Mem. Geol. Surv., vol. iii., p. 545, pl. xi. B, fig. 15. 
Cucullella ? Siluria, third edition, p. 50; Foss. 8, fig. 2. 
From Mem. Geol. Surv., vol. iii., pl. xi. B, fig. 15 a, upper figure ; both 
figures being marked with the same letter; the lower one should probably 
have been 15 d. 
Lower LianpeILo.—Lord’s Hill, Shelve. 
Fic. 9.—Ripib2iA COMPLANATA, Salter. 
Mem. Geol. Surv., vol. iii., p. 346, pl. xi. B, fig. 16. 
Redonia ? Siluria, third edition, p. 50, Foss. 8, fig. 3. 
Ribeiria. Ibid., p. 549. 
From Mem. Geol. Surv., vol. iit, pl. xi. B, fig. 16. 
Lower LuanpeILo.—Lord’s Hill, Shelve. 
GASTEROPODA, 
Fic. 10.—a, 6. Evomruatus Cornpensis, Sowerby. 
Silurian System, pl. xxii., fig. 16 ; Siluria, third edition, pl. vii., fig. 5, 5 a. 
From original figure ia Silurian System, pl. xxii., fig. 16. 
LLANDEILO Rocxs.—Corndon Hills. 
Fig. 11.—2, b, c. OPHILETA CoMPACTA, Salter. 
Journ. Geol. Soc., vol. xv., p. 378, pl. xiii., fig. 12. 
Siluria, third edition, p. 217; Foss. 38, fig. 4. 
From the original figure in Journ. Geol. Soc., cited. 
a. Lower surface. 0. The convex cast. ce. Upper concave surface. 
LLANDEILO Rocks.—Durness, in Sutherland, North-western Highlands. 
HETEROPODA. 
Fig. 12.—a, 6. BELLEROPHON PERTURBATUS, Sowerby. 
Euomphalus. Silurian System, pl. xxii., fig. 15. 
Euomphalus fureatus, M‘Coy, Sil. Foss., Ireland, p. 13, pl. i., fig. 11. 
