Terebratula. 



MOLLUSCA. 



131 



Transversely oval, gibbous ; beaks produced, and incurved ; 

 hinge line short ; surface with about twelve sulcatcd, laminx 

 thin edges, lying close upon eacii 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. 2 1 , 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, Walthen, 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- 

 nam, 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 XL— COMPOSIT A.— Brown. 



Shell somewhat pentan<rular ; 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 ambiguus of Sowerby, .nnd 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. 



I. 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 XIL— TEREBRATULA.— i?/-M^M«-^re. 



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. lb. Pal. Fos. p. 91, 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 iu its outline. Var. b obovate, edges 

 blunt, smaller, deeper, and less concave towards the base. 



Carboniferous Limestone, Holland, 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. 



