Leptvena. 
MOLLUSCA. 
121 
45. Orthis intercostata —The Inter-ribbed Orthis, pi. 
LIII. fig. 43. 
Orthis intercostata . Portlock, Geo. Rep. p. 454, pi. 37, 
fig. 3. 
Nearly orbicular; hinge area triangular, its height being 
equal to about a fourth of the width; surface with fine, thread¬ 
like, divergent ribs, about sixteen of which have finer inter¬ 
vening striae, but with those next the unibones equal. 
Silurian Strata, Desertcreat, Tyrone, Ireland. 
46. Orthis lens —The Lens-shaped Orthis, pi. LIII. 
fig. 44, 45. 
Orthis lens. Phillips, Pal. Fos. p. 65, pi. 26, fig. 110, a, h. 
Suborbicular, much compressed, valves equally convex; lower 
valve with a mesial sulcus near the umbo, and prolonged in a 
shallower furrow towards the base; external surface with about 
twenty undulated striae, narrower than the intervening spaces, 
which arc striated transversely. 
Devonian Shales at Hope, near Torquay. 
47. Orthis parallela. —The Parallel Orthis, pi. LIII. 
fig. 49. 
Orthis parallela. Phillips, Pal. Fos. p. 64, pi. 26, fig. 109> 
a , by c, d. 
Oblong, sub ovate, much compressed, broadest towards the 
base; hinge line about half the breadth of the valves; umbones 
produced; deeper valve a little tumid on the mesial line, and 
somewhat hollowed on the other; subrostral ridges of the 
deeper valve much lengthened, almost parallel, and including a 
considerably lengthened, divided oval area; whole surface 
covered with numerous, sharp, radiating striae, of unequal length 
and thickness, with several transverse, well-marked lines of 
growth. 
Devonian Shales at Pilton and Brushford, North Devon; and 
South Petherwin, Cornwall. 
48. Orthis cancellata —The Cancellated Orthis, pi. 
LIII. fig. 46. 
Orthis cancellata. Portlock, Geo. Rep. p. 450, pi. 32, fig. 
19. 
Suborbicular, compressed; hinge line same width as the 
valves; umbones but slightly produced; whole surface with 
numerous, fine, somewhat elevated, radiating ribs, about 
twenty-five in number, with four or five finer intervening, 
longitudinal striae; the whole surface crossed by numerous, 
fine, concentric stria), producing an elegant cancellated appear¬ 
ance. 
Silurian Strata at Desertcreat, County of Tyrone, Ireland. 
49. Orthis interstrialis —The Interstriated Orthis, pi. 
LIII. fig. 48. 
Orthis interstrialis. Phillips, Pal. Fos. p. 61, pi. 25, fig. 
103. 
Semicircular; hinge line parallel, and considerably broader 
than any other part of the valves, forming subauriform pro¬ 
cesses; one valve uniformly convex, the other depressed; 
whole surface with numerous, sharp, radiating striae, of unequal 
length, with very numerous, much finer, intermediate ones; 
on the flatter valve the striae are stronger and more elevated 
towards the umbo, and assume the character of furrows towards 
the margin. 
Devonian Shales, Barton, South Devon. 
50. Orthis Calcar. —The Spur Orthis, pi. LIII. fig. 55. 
Orthis calcar. Phillips, Pal. Fos. p. 138, pi. 58, fig. 112.** 
Semicircular, a little elongated; hinge line equal to the 
breadth of the valves; whole surface covered with about twelve 
granulated, indistinct, divergent ribs, which become strongly 
marked towards the margins of the valves, and being regularly 
defined, resembles a fringe all round. 
Devonian Shales at Pilton, North Devon. 
51. Orthis Pecten —The Combe Orthis, pi. LIII.* 
fig. 1. 
Orthis plicata. Sowerby, Sil. Syst. p. 53, pi. 21, fig. 9. 
Somewhat elongated, compressed ; hinge line fiat the whole 
breadth of the shell; umbones not elevated; sides nearly 
parallel; base gently rounded; whole surface covered with 
numerous, radiating stria), crossed by many, nearly equidistant, 
remote lines of growth. 
Lower Silurian Limestone at Coniston. 
Genus IX—LEPTCENA Dolman. 
Shell equilateral, and inequivalve; one valve being 
convex for the most part, and very rarely somewhat 
depressed; its anterior edge rounded, very thin, deflected 
or bent downwards, and produced into an irregularly 
cylindrical form, a little expanded towards its lower 
edge; the opposite valve is usually flat, or slightly con¬ 
cave on the outside, with its anterior margin reflected, 
so that its inner edge lies against the inside of the con¬ 
cave valve; the cardinal margin is transverse, parallel 
and linear, sometimes so much produced on both sides as 
to give it a winged appearance; hinge with two some¬ 
what tooth-like processes in the upper valve, and the 
under valve with a crenulated, internal hinge line in 
most species, which is provided with two elevations, 
bounding the cicatrices of the muscles. 
1. Leptasna analoga. —The Analogical Leptama, pi. 
LIII.* fig. 10. 
Leptcena analoga. Phillips, Geo. York. pi. 7, fig. 10. Ib. 
Pal. Fos. p. 56, pi. 24, fig. 93. Sowerby, Geo. Trans. V. 2nd 
series, pi. 56, fig. 3. Ib. Min. Conch. VII. p. 9, pi. 615, 
fig. 1. 
Semicircular, compressed; hinge line generally straight, or 
sometimes slightly concave, prolonged into pointed auriform 
processes; lower valve slightly convex near the umbo; flattened 
on the disk near the base concentrically, and angularly bent 
towards the upper valve; surface somewhat corrugated, with 
flexuous, rounded wrinkles, which are somewhat irregular on 
the ears; the whole crossed by pretty equal, rounded, straight, 
radiating stria). Length about an inch. 
Found in the Carboniferous and Mountain Limestone at 
Bolland, Cork, Barnstaple, and Plymouth. 
2. LepTj-ena caperata. —The Wrinkled Leptama, pi. 
LIII * fig. 7. 
Leptcena cajicrata. Sowerby, Geo. Trans. V. 2nd series, pi. 
53, fig. 4. Phillips, Pal. Fos. p. 58, pi. 25, fig. 98. 
2 H 
