120 
MOLLUSCA. 
Orthis. 
Transversely semicylindrical, depressed; base somewhat 
straight; sides rounded; surface with linear, unequally thick, 
divergent stria?. Length five lines ; breadth nine lines. 
Nearly allied to LepUena lata , but differs in both valves being convex, 
in beiug destitute of spines on the hinge, and in the unequally sized stria?. 
Lower Silurian llocks, Gorllwyn; Goleugoed and Berwyns, 
Caermarthenshire. 
36. Orthis alata. —The Winged Orthis, pi. LIII. fig. 
13, 14. 
Spii'ifer alatus. Sovvcrby, Sil. Syst. p. 638, pi. 22, fig. 7, 
upper figures. 
Semicircular; hinge line parallel, with extended, cuspidate, 
auriform processes, slightly inflated in the middle of the valves; 
surface with about eighteen acute, radiating plaits, larger in the 
centre of the valves, and smaller and closer towards their upper 
portions; sides slightly crenated. Length five lines and a half; 
width nine lines and a half. 
Lower Silurian Rocks, Mount Pleasant and Pensarn, Caer- 
marthen. 
37. Orthis pennatus. —The Unequal-winged Orthis, pi. 
LIII. fig. 4, 5. 
Spii'ifer alatus . Sowerby, Sil. Syst. p. 638, pi. 22, fig. 7> 
lower figures. 
Longitudinally semiovate, oblique, inflated; hinge line paral¬ 
lel, extended on cither side into long, auriform processes, one 
of which is considerably longer and more acute than the other; 
surface with numerous, acute, arcuated, radiating ribs, which 
are smaller and more numerous towards the margins, with two 
or three remote, slightly marked lines of growth; margins 
slightly crenated. Length six lines; width seven lines. 
Lower Silurian Rocks, Mount Pleasant, Caermarthen. 
38. Orthis interliniata —The Interlinear Orthis, pi. 
LIII. fig. 1, 2, 3. 
Orthis interliniata . Sowerby, Geo. Trans. V. 2nd series, pi. 
53, fig. 11, and pi. 54, fig. 14. Phillips, Pal. Fos. p. 63, pi. 26, 
fig. 106. 
Transversely elliptical, much compressed; larger valve not 
very convex; beak a little prominent; smaller valve with a 
shallow depression; hinge line little more than half the width 
of the valves; base nearly straight; surface with numerous, 
fine, filiform, radiating, unequally long stria?, which are stronger 
towards the margins of the valves; convex valve with nearly 
equal muscular impressions, and the subrostral plaits arcuated 
so as to include a cordiform area; impressions of the cardinal 
teeth in the other valve broad. 
Sowerby remarks as to this species, that it forms a link serving to 
connect five other species. It approaches O. lata in its wide form, and 
irregularity of its stria?; it resembles O. orbicularis and O. canalis in the 
depression of the cardinal teeth of the flatter valves, and these species are 
exact analogues of O. lunata and O. testudinaria. 
Abundant in the Devonian Shales at Petherwin, Croyde, and 
Leary, North Devon; Barnstaple, Morebath, and Landlake, 
Cornwall. 
39* Orthis parallela. —The Parallel Orthis, pi. LIII. 
fig. 9 and 16. 
Orthis parallela. Phillips, Pal. Fos. p. 64, pi. 26, fig. 109, 
a , 6, c, d. 
Oblong-oval, considerably compressed; hinge line narrow, 
occupying about half the width of the valves; base wide; deeper 
valve with a slightly tumid, mesial line; flatter valve with a 
hollowed mesial depression; surface with numerous, sharp, 
unequally long and short, radiating stria?, crossed by lines of 
growth; subrostral ridges of the deeper valve parallel, and 
much lengthened, and including a long, divided area. 
Devonian Shales, Pilton and Brushford, North Devon ; and 
Petherw'in, Cornwall. 
40. Orthis granulosa —The Granular Orthis, pi. LIII. 
fig. 15. 
Orthis granulosa. Phillips, Pal. Fos. p. 65, pi. 26, fig. 111. 
Nearly orbicular, considerably compressed, and lenticular; 
hinge line somewhat more than half the width of the valves; 
surface with numerous, fine, granulated, unequally long stria?, 
increasing to double the number towards the margin, and pro¬ 
ducing a bordered aspect. 
Devonian Shales at Hope, near Torquay, South Devon. 
41. Orthis arcuata —The Arquated Orthis, pi. LIII. 
fig. 23. 
Orthis arcuata. Phillips, Pal. Fos. p. 64, pi. 26, fig. 107. 
Transversely oblong-ovate, very much compressed; one 
valve uniformly convex, the other with a slight mesial furrow; 
whole surface with very fine, divergent stria?, arcuated towards 
the sides. 
This species is subject to variety: var. a with the suleated valve flat; 
var. by the suleated valve convex on both sides of the mesial furrow. 
Distinguished from O. interliniata by its more lengthened shape, and 
greatly arcuated and very fine stria?. 
Devonian Shales, Hope, near Torquay. 
42. Orthis longisulcata. —The Long-furrowed Orthis, 
pi. LIII. fig. 37. 
Orthis longisulcata. Phillips, Pal. Fos. p. 62, pi. 26, fig. 
105. 
Transversely elliptical, compressed; sides rounded; hinge 
line a little arcuated; surface with very numerous, fine, divari¬ 
cating stria', which are interrupted by concentric, imbricated, 
distant lines of growth; internal plates divergent, situate near 
the beak of the lower valve. 
Devonian Shales, Watersmeet; Woodabay; West Lee, and 
Linton, North Devon. 
43. Orthis concentrica —The Concentric Orthis, pi. 
LIII. fig. 41. 
Orthis concentrica. Portlock, Geo. Rep. p. 452, pi. 37, 
fig. 1. 
Semicircular, compressed; hinge line nearly parallel; mus¬ 
cular impressions deeply furrowed, internally plaited near the 
margins; surface with fine, divergent, filiform stria?. 
Silurian Strata, Tyrone, Ireland. 
44. Ortius umbraculum —The Shaded Orthis, pi. LIII. 
fig. 32, 33. 
Orthis umbraculum. Portlock, Geo. Rep. p. 456, pi. 37, 
fig. 5. 
Almost semicircular; hinge line nearly parallel; lower valve 
slightly convex towards the beak, but nearly flat at the margin; 
cardinal area low, and strongly suleated; upper valve flat, with 
a low, triangular, cardinal area; surface with twelve or thirteen 
filiform costa?, emanating from the umbones, and radiating 
towards the margins, with very numerous, extremely fine, 
intervening stria?, the dichotomy being by insertion, and not by 
furcation; besides the stria?, by the aid of a lens, extremely 
fine, longitudinal lines are observable. 
Shale of the Silurian series, Fermanagh, Ireland. 
