118 
MOLLUSCA. 
Orthis. 
12. Orthis plicata. —The Plicated Orthis, pi. LII.* 
fig. 61. 
Orthis plicata . Sowerby, Geo. Trans. V. 2nd series, pi. 53, 
fig. 10. 
Transversely elongated, depressed, with numerous sharp 
plaits. Width twice its length. 
Found in the Devonian Shales at Barnstaple. 
13. Orthis tenuistriata —The Thin-striated Orthis, pi. 
L1II. fig. 11, 12. 
Orthis tenuistriata. Sowerby, Geo. Trans. V. 2nd series, pi. 
57, fig. 12. 
Semicircular; base straight, with numerous, very fine striae ; 
one valve convex, the other considerably flatter; hinge area 
narrow and parallel. 
Found in the Devonian Shales at Morebath. 
14. Orthis orbiculata —The Orbicular Orthis, pi. LIII. 
fig. 6, 7, 8. 
Orthis orbicularis . Sowerby, Sil. Syst. p. 611, pi. 5, 
fig. 16. 
Nearly orbicular, with fine, regular, deep, radiating striae; the 
larger valve very convex, with a slightly curved beak, furnished 
internally with a straight, longitudinal ridge, with a curved one 
on either side; the other valve slightly convex, with a wide, 
central depression ; hinge area very small. Length six lines; 
width seven lines. 
Abundant in the Upper Ludlow Rock at Ludlow; Delbury; 
Sutton, near Wenlock; Dog Hill, near Ledbury; and Cwm- 
nantgwyn, near Buleth. 
15. Orthis canalis. —The Canaled Orthis, pi. LIII. fig. 
34, 35, 36. 
Orthis canalis. Sowerby, Sil. Syst. p. 640, pi. 20, fig. 8, and 
pi. 13, fig. 12 a. 
Longitudinally semi ovate; one valve very convex, beak pro¬ 
duced, pointed, and incurved; the other rather flat, and with a 
broad central furrow, a little convex along the sides; base some¬ 
what pointed, and slightly depressed; hinge line not so wide as 
the valves; surface with many fine, radiating striae, which are 
more numerous towards the margins. Length and width six 
lines and a half. 
Differs from O. elegantula in its more elongated form, and in the beak 
of the larger valve being longer and more incurved. 
Wenlock Shale, Tame Bridge, Woolhope, and Delves Green; 
and also in the Cardoc Sandstone at Horderley and Whittings- 
low, near the Cardoc, See. 
16. Orthis testudinaria —The Tortoise Orthis, pi. 
LII* fig. 10. 
Orthis testudinaria . Dalman, p. 115, pi. 2, fig. 4. Sowerby, 
Sil. Syst. p. 640, pi. 20, fig. 9. 
Nearly orbicular; with numerous granulated radii of unequal 
length; larger or upper valve very convex, being nearly sub¬ 
conic, with an incurved beak; the lower valve with a mesial 
furrow; hinge line almost as wide as the valves. Length six 
lines and a half; width eight lines. 
rhis differs from O. elegantula in being more convex, and in the radia¬ 
tions being stronger. It also differs in its internal structure. 
Found in the Lower Silurian Rocks at Gaerfawr, east and 
south of Cardoc and Powis Castle. 
17. Orthis Lunata. —The Moon-shaped Orthis, pi. LIII. 
fig. 56, 57, 58. 
Orthis Pecten? Dalman, 1. c. p. 110, pi. 1, fig. 6. Hist. 
Pet. Suec. p. 70, pi. 20, fig. 6. Sowerby, Sil. Syst. p. 638, pi. 
21, fig. 9. 
Semioval, convex; with numerous, nearly equal, fine, slightly 
raised stria?, intercepted by almost equidistant lines of growth; 
hinge line almost as wide as the shell; one valve nearly flat. 
Length one inch and a half; width one inch and eleven lines. 
18. Orthis Pecten?— -The Pecten-formed Orthis, pi. 
LIII* fig. 1. 
Orthis Pecten, var. Dalman, pi. 1, fig. 6. Hist. Pet. Suec. 
pi. 20, fig. 6. Sowerby, Sil. Syst. p. 614. 
Transversely ovate; depressed, with many sharp, radiating 
sulci, with intermediate ones towards the margins. Length ten 
lines and a half; width one inch and four lines. 
Sowerby says this is a much wider shell than the true O. Pecten. 
Found in the Aymestry Limestone, Aymestry and Coniston. 
19. Orthis rustica —The Rude Orthis, pi. LIII. fig. 17. 
Orthis rustica. Sowerby, Sil. Syst. p. 624, pi. 12, fig. 9. 
Transversely subquadrate, depressed; hinge area rather large, 
and triangular; surface uneven, with from forty to fifty rounded, 
divergent ribs, and intermediate ones as they approach the 
margins; base nearly straight. Length one inch and one line; 
width one inch and a half. 
Wenlock Limestone, Wenlock and Valley of Woolhope. 
20. Orthis alternata— The Alternately-ribbed Orthis, 
pi. LIII. fig. 18, 19. 
Orthis alternata. Sowerby, Sil. Syst. p. 624 and p. 638, pi. 
19, fig. 6. 
Iransversely obovately subquadrangular; with extremely nu¬ 
merous, fine, unequal, raised striae, increasing in number towards 
the margins; hinge line shorter than the width of the shell. 
Length ten lines; width thirteen lines. 
Lower Silurian Rocks, Whittingslow; Cardoc, Soudley; 
Lower Lickey Ridge; Berwyns, See. 
21. Orthis protensa.—T he Stretched-out Orthis, pi. 
LIII. fig. 21. 
Orthis protensa. Sowerby, Sil. Syst. p. 638, pi. 22, fig. 8, 9. 
Semiovate, depressed; hinge line nearly the width of the 
valves; unequally thick; surface covered with sharp, linear, 
divergent striae, crossed by a few remote lines of growth. 
Length eight lines; width seven lines. 
Lower Silurian Rocks, Berwyns; Golcugoed, and Meadow 
Town, near Shelve. 
22. Orthis compressa —The Compressed Orthis, pi. 
LIII. fig. 20. 
Orthis compressa. Sowerby, Sil. Syst. p. 38, pi. 22, fig. 12. 
Semiovate, lenticular, compressed; hinge line parallel; whole 
surface covered with very numerous, close-set, punctated stria?. 
Length one inch; width fourteen lines. 
Lower Silurian Rocks, Hope Quarry, near Shelve, Shrop¬ 
shire. 
23. Orthis semicircularis —The Semicircular Orthis, 
pi. LIII. fig. 30, 31. 
Oi'this semicircularis. Sowerby, Sil. Syst. p. 639, pi. 21, 
%. 7. 
Semicircular, convex; base slightly rounded; surface covered 
with about thirty sharp, radiating striae, increasing in number 
towards the margin; umbo protruding. Length three lines and 
a half; width half an inch. 
