Terebratula. 
MOLLUSCA. 
131 
Transversely oval, gibbous; beaks produced, and incurved ; 
hinge line short; surface with about twelve sulcated, laminae 
thin edges, lying close upon each other, and having longitudinal 
furrows. 
Carboniferous Limestone, Derbyshire; and at Settle, York¬ 
shire. 
39- Atrypa orbicularis— The Orbicular Atrypa, pi. 
LIV. fig. 29. 
Atrypa orbicularis . Sowerby, Sil. Syst. p. 637, pi. 19, fig. 
3,4. * 
Suborbicular; valves equal; a little wider than long, with a 
slight sinus in the base, and numerous forked furrows, the inter¬ 
vening ridges not scaly. Length seven lines; width eight lines. 
Somewhat like Atrypa aspera, but smoother. 
Lower Silurian Rocks, Gorllwynfach ; Conygree Coppice; 
Woodford Hill; Abberley; and Melvern Ridge, End Hill. 
40. Atrypa undata —The Waved Atrypa, pi. LIV. fig. 
76, 77. 
Atrypa undata . Sowerby, Sil. Syst. p. 637, pi. 21, fig. 2. 
Transversely elliptical, inflated, and smooth; one valve with a 
central elevation leading to a tongue-shaped sinus in the edge; 
and with a corresponding projection in the other. Length ten 
lines; width one inch and four lines. 
Lower Silurian Limestone, Cefn Rhyddan, Llandovery; and 
Robeston, Walt hen, Pembrokeshire. 
41. Atrypa Lens. —The Lens-formed Atrypa, pi. LIV. 
fig. 68, 69. 
Atrypa lens . Sowerby, Sil. Syst. p. 637, pi. 21, fig. 3. 
Suborbicular, compressed, smooth, with obscure radiations; 
the upper valve elevated along the middle. Length about two 
inches and three-quarters; width nearly two inches. 
Lower Silurian Rocks, north end of Snead’s Heath, Mundi- 
11 am, and Cefn Rhyddan, Llandovery. 
42. Atrypa crassa. —The Thick Atrypa, pi. LIV. fig. 
38, 39. 
Atrypa crassa . Sowerby, Sil. Syst. p. 636, pi. 21, fig. 1. 
Spherical, smooth, very thick; with three very deep, muscu¬ 
lar impressions, the central one tongue-shaped, and striated; 
the lateral ones with five or six more or less deep furrows. 
Lowest Silurian beds, Cefn, Rhyddan, Caermarthenshire. 
43. Atrypa obovata —The Obovate Atrypa, pi. LIV. 
fig. 40, 41. . 
Atrypa obovata . Sowerby, Sil. Syst. p. 618, pi. 8, fig. 8, 9* 
Transversely obovate, convex, smooth; beaks small, con¬ 
tiguous; base with a marginal elevation in one valve, producing 
a rounded sinus in the edge of the other. Length five lines; 
width five lines and a half. 
Lower Ludlow Rocks, Mathon Lodge, Malvern Hills. 
Genus XI .— C OM P O S 1 T A.— Brown . 
Shell somewhat pentangular; hinge line very short; 
beak of the larger valve produced, with a small circular 
perforation; inside furnished with spiral appendages. 
This genus is founded upon the Spirifer ambiyuus of Sowerby, and is 
intermediate between that genus and Terebratula. The perforated beak 
removes it from Spirifer , and the internal spiral appendages never exist 
in the genus Terebratula , but are peculiar to the genus Spirifer. 
1. Composita ambigua. —The Ambiguous Composita, pi. 
LIV.* fig. 6, 7. 
Spirifer ambiguus . Sowerby, IV. p. 105, pi. 376. 
Subpentangular; beak considerably produced, and perforated; 
hinge line extremely short; sides slightly rounded; a wide 
mesial furrow in the larger valve, with a corresponding ridge in 
the other; base three-sided ; whole surface smooth. 
Mountain Limestone, Derbyshire, Northumberland, and Pem¬ 
brokeshire. 
Genus XII.—TEREBRATULA.— Bruguiert. 
Shell inequivalve, equilateral, generally trigonal and 
gibbous; attached by a short peduncle to extraneous 
marine bodies; the larger or upper valve with a project¬ 
ing umbo, frequently bent, and perforated at its apex, 
or notched at its inner edge, and having a small curved 
tooth on each side of its hinge, which fits into a corres¬ 
ponding pit in the opposite valve; the inside of the 
smaller valve is provided with two slender testaceous 
processes, which are sometimes simple, short, and re¬ 
curved; at others considerably elongated, branched, bent 
in various directions, and anastomosing for the most part; 
sometimes they are situate near the centre of the valve, 
and in other instances are united by their points to the 
shell; these usually emanate from each side of the hinge; 
both valves provided with two nearly obsolete, muscular 
impressions, but sometimes they are strongly developed; 
those of the larger or perforated valve are oblong, central, 
and close to each other; in the smaller valve they are tri¬ 
angular, with their angles rounded, also nearly central, 
but more distant than in the other valve. 
DIVISION I.—GENERALLY OBLONG, AND SMOOTH; THE MIDDLE 
OF THE FRONT EVEN, OR DEPRESSED. 
1. Terebratula hastata. —The Spear-shaped Terebra¬ 
tula, pi. LII. fig. 9, 10, and pi. LIV.* fig. 24. 
T. hastata . Sowerby, V. pi. 446, fig. 2, 3. Phillips, Geo. 
York. II. pi. 12, fig. 1. Ib. Pal. Fos. p. 9L pi* 35, fig. 168. 
Elongated, elliptical, semicompressed; valves nearly equal: 
base truncated, and indented, in which situation it is a little 
concave ; edges sharp. Width about two-thirds its length. 
Subject to considerable variety in its outline. Var. b obovate, edges 
blunt, smaller, deeper, and less concave towards the base. 
Carboniferous Limestone, Bolland, Derbyshire, Otterburn, 
and Bristol; and Queen’s County, Ireland. 
2. Terebratula indentata —The Indented Terebratula, 
pi. LII. fig. 11, 14, and 20. 
T. indentata . Sowerby, V. p. 65, pi. 445, fig. 2. Zeit. pi. 
39» fig- 8) and pi. 44, fig. 3. 
Elliptical, its length a half more than its width, smooth, more 
or less inflated; valves equally convex; beak small, and much 
incurvated; base with a deep, obtuse-angular notch; each valve 
with rather broad furrows, extending into about a third their 
length ; the two sides not always equal. 
Found in the Fullers’ Earth, Banbury, in Oxfordshire. 
