Orthis. 
MOLLUSCA. 
117 
Found in the Devonian Shale at Combe Martin, Hagginton, 
Bradley, and Ogwell. 
Genus VIII.—ORTIIIS.— Dalman . 
Shell inequivalve, with a rectilinear hinge; umbones 
distant; larger valve with a transverse, smooth area, and 
a triangular pit. 
Distinguished from Spirifer by the long narrow hinge, 
and circular flat form of the striated shells. 
1 . Orthis Arachnoidea —The Spider’s-web Orthis, pi. 
LII. fig. 19. 
Orthis arachnoidea . Phillips, Pal. Fos. p. 67, pi. 27, fig. 
114. Spirifer arachnoidea , lb. Geo. York. II. p. 220, pi. 11 , 
fig. 4. 
Shield-shaped, much compressed; hinge line nearly parallel, 
and as wide as the shell; umbones very small, and blunt; upper 
valve a little convex; whole surface covered with fine, sharp, 
divergent stria?, which are crossed at intervals by remote lines 
of growth. 
Mountain Limestone, Ilaltwhistle, Stradone, Allenheads, and 
near Hesket, Newmarket, South Devon and Hope, Torquay. 
2 . Orthis subarachnoidea —The Spider Web-like Or¬ 
this, pi. LIII. fig. 27. 
Orthis subarachnoidea . Vernon, Geo. Trans. 2nd series, VI. 
pi. 36, fig. 3. Orthis arachnoidea , Phillips, Pal. Fos. p. 67, pi. 
27, fig. 114. 
Elongated; hinge line nearly parallel, and equal to the width 
of the valves; lesser valve convex; surface with very numerous, 
continually subdivided and resubdivided stria?, arcuated near 
the hinge, and a few of which are more prominent than the 
others. 
Devonian Shale, Hope, near Torquay. 
3. Orthis anomala. —The Anomalous Orthis, pi. LIII. 
fig. 28. 
Orthis anomala. Sowerby, Sil. Syst. p. 638, pi. 21 , fig. 10 . 
Anomites anomalus, Schl. Nacht. Pet. p. 65, pi. 14, fig. 2 . 
Longitudinally oblong; convex; umbones obtuse; sides nearly 
straight; hinge line almost as wide as the valves; surface with 
very numerous, longitudinal striae; base slightly rounded. 
Length one inch and seven lines; width one inch and five 
lines. 
Lower Silurian Rocks, Cardock; Berwyns and Ilorderley. 
4. Orthis filiaria —The Thready Orthis, pi. LII. fig. 3. 
Spiriferajiliaria. Phillips, II. p. 220, pi. 11, fig. 3 . 
Slightly elongated, nearly pocket-shaped, much compressed, 
narrow above; hinge line short; cardinal area very narrow ; 
umbones greatly blunted; a shallow mesial furrow; surface with 
rather wide-set, radiating, filamentary processes. 
Mountain Limestone, Bolland, Fountains’ Fell, Dowall, Der¬ 
byshire, and Otterburn. 
5. Orthis connivens. —The Connivant Orthis, pi. LII. 
fig. 13. 
Spirifera connivens. Phillips, II. p. 220, pi. 11 , fig. 2 . 
Subglobose, with an undulated margin; whole surface covered 
with coarse, waving, divergent, longitudinal stria?. 
Mountain Limestone, Bolland and Pembrokeshire. 
6 . Orthis grandis —The Great Orthis, pi. LII* fig. 
1 , 2 . 
Orthis grandis. Sowerby, Sil. Syst. p. 638, pi. 20 , fig. 
12, 13. 
Greatly compressed, semioval, short; with numerous inter¬ 
nal bifurcate radiations. Length one inch and a half; breadth 
two inches. 
Found in the Lower Silurian Limestone at the Flank of 
Cardoc, Ilorderley, and Acton Scott. 
7. Orthis elegantula —The Elegant Orthis, pi. LII* 
fig. 3, 4. 
Orthis canalis. Sowerby, Sil. Syst. p. 640, pi. 20 , fig. 8 . 
Transversely semioval; larger valve very deep, with an acute 
incurved beak; smaller valve with a concave mesial furrow, and 
slightly convex along the sides; base somewhat pointed, and 
much compressed; hinge line a little shorter than the width 
of the valves; whole surface covered with fine radiating stria?. 
Length and breadth six lines and a half. 
Found in the Wenlock Shale at Croft; Delves Green; Wool- 
hope and Falfield, near Tortworth; and in the Cardoc Sand¬ 
stone at Whittingslow', Horderley, &c. 
8 . Orthis Yihgata. —The Branched Orthis, pi. LII.* 
fig. 7. 
Orthis virgalus. Sowerby, Sil. Syst. p. 639, pi. 20 , fig. 15. 
Transversely obovate, with about thirty rounded, smooth 
radii; hinge line shorter than the breadth of the valves, and 
slightly arcuated. Length eight lines and a half; width eleven 
lines. 
Found at Acton Scott; Llanwyth, Builth, and Horderley, in 
the Lower Silurian Rocks. 
9. Orthis Vespertilio. —The Bat Orthis, pi. LII.* fig. 
8 , 9. 
Orthis Vespertilio. Sowerby, Sil. Syst. p. 640, pi. 20 , fig. 
11 . 
Semicircular; with numerous, thin, radiating ridges; upper 
valve a little convex, with a broad, angular, longitudinal, central 
rib; lower valve convex, with a deep mesial furrow; sides an¬ 
gular, at the ends of the hinge line. Length three-quarters of 
an inch; width one inch and three lines. 
Found in the Lower Silurian Rocks at Cortor, near Clun- 
burg; Acton Burnell and Stevens Hill, in the Cambrian Packs 
at Bala, &c. 
10 . Orthis triangularis —The Triangular Orthis, pi. 
LII* fig. 14. 
Orthis triangularis. Sowerby, Sil. Syst. p. 640, pi. 20, fig. 
17. 
Triangular, rounded in front, convex; surface with numerous, 
fine radiations. Length four lines and a half; width five lines. 
Found in Volcanic Grit, Lower Silurian Rocks at Marring- 
ton Dingle, near Chirbury. 
11 . Orthis Flabellulum —The Little Fan Orthis, pi. 
LII.* fig. 39, 40. 
Orthis Flabellulum, Sowerby, Sil. Syst. p. 639, pi. 21, fig. 8. 
Transversely subovate; hinge line slightly arcuated, not so 
wide as the valves; one valve fiat, the other convex, with a 
slight mesial channel; surface with about twenty-four rounded 
radii. Length eight lines and a half; width thirteen lines. 
Found in the Cardoc Sandstone at Corton, Clunbury; and at 
Bala and Snowdon, in the Cambrian Rocks. 
2 g 
