CLASS SECOND. 



CONCHIFERA; OR BIVALVES. 



Animals soft, inarticulate, destitute of a head or organs 

 of \ision, and always fixed within a bivalve shell ; pro- 

 vided with external branchiae, their circulation is simple, 

 and heart unilocular. 



All the species are aquatic, living either in the sea or 

 fresh waters. None of the animals have an internal 

 shell, the body is invariably soft, and the mouth is situate 

 near the left side of the hinge. 



Grand-Division I. 



Ligament none or unknown, or in its Stead a tendinous 

 chord, which supports the shell. 



ORDER I.— MONOMYARIA. 



Animals provided with but one muscle of attachment, 

 or adductor muscle, which leaves one subcentral muscu- 

 lar impression inside of each valve. 



FAMILY L— BRACHIOPODA. 



Shell bivalve, adhering to extraneous marine bodies, 

 either by the shell itself being in contact with them, or 

 attached by a tendinous chord. Shells not quite equi- 

 valve, and open by a hinge. 



Genus I — LINGULA Bruguiere. 



Shell equivalve, equilateral, oblong-ovate, compressed, 

 thin ; acute and gaping at the umbones ; slightly trun- 

 cated or trilobate at the base ; muscular impressions 

 situate towards the centre of the valves; external surface 

 covered w ith a glossy, thick epidermis ; hinge destitute 

 of teeth ; shell suspended by a cylindrical, fleshy, tendi- 

 nous pedicle, attached to the umbones. 



1. LiNGULA ovALis. — The Oval Lingula, pi. XLIX. fig. 2. 



Lingula ovalis. Sowerby, I. p. 56, pi. 19, fig. 4. Fleming, 

 p. 368. 



Oblong-oval, smooth, depressed ; beaks rounded and blunt ; 

 base broad and circular. Length half an inch ; breadth a 

 quarter. 



London Clay, Pakefield, Suffolk. 



2. Lingula ellu'tica — The Elliptical Lingula, pi. XLIX. 

 fig. 3. 



Lingula elliptica. Phillips, II. p. 221, pi. 1 1, fig. 15. 



An elongated ellipsis, retrally acuminated; surface plane, with 

 wide-set, slender striae, radiating from the umbones ; basal line 

 rather acute. 



Mountain Limestone, Ashford, Derbyshire. 



3. Lingula squamiformis. — The Scale-shaped Lingula, 

 pi. XLIX. fig. 4. 



Lingula squamiformis. Phillips, II. p. 221, pi. 11, fig. 14. 



Oblong; umbones acuminated; base truncated; superior por- 

 tion of the valves inflated, compressed below ; an oblong-oval 

 depression in the centre; sides parallel; surface with longitudi- 

 nal and concentric lines, and with radiating stria> at the base. 



4. Lingula Mytilloides. — The Mjtilus-likc Lingula, pi. 

 XLIX. fig. 6. 



Lingula Myliloides. Sowerby, I. p. 55, pi. 19, fig. 1, 2. 

 Fleming, p. 3G8. 



Oval, smooth, shining; umbones obtuse; narrower above, and 

 well rounded at the base, where it is somewhat flattened. 



Carboniferous Limestone of Durham, &c. 



5. Lingula Beanii. — Bean's Lingula, pi. XLIX. fig. 7. 

 Lingula Beanii. Phillips, I. p. 128, pi. II, fig. 24. 

 Oblong-ovate, smooth, glossy; somewhat narrow above, with 



projecting beaks, which are somewhat obtuse at the point; sides 

 nearly parallel; base rounded; surface with delicately marked 

 lines of growth. 



Blue Wick of the Inferior Oolite. 



6. Lingula parallela. — The Parallel Lingula, pi. XLIX. 

 fig. 11 and 15. 



Lingula parallela. Phillips, II. p. 221, pi. 11, fig. 17, 18, 19. 



Ovate, nearly equal at both extremities, front a little more 

 rounded than the other end; umbones a little elevated, but not 

 projecting beyond the extremity ; surface with shallow lines of 

 growth. Fig. 11, the flatter valve; fig. 15, the deeper one. 



Mountain Limestone, Northumberland. 



7. Lingula marginata. — The Marginated Lingula, pi. 

 XLIX. fig. 12. 



Lingula marginata. Phillips, II. p. 221, pi. 11, fig. 16. 



Much elongated, truncated in front, retrally rounded; edges 

 of the valves turned up; sides parallel; valves flattened on their 

 centres, with an elevated mesial ridge ; whole surface covered 

 with small, oval, hollow, fine, concentric and radiating stria;. 



The Mountain Limestone at Bowes. 



8. Lingula scutifokmis The Scuttle-shaped Lingula, 



pi. XLIX. fig. 20. 



Lingula parallela. Phillips, II. p. 221, pi. 11, fig. 18. 



Scuttle-shaped; truncated behind, and produced in front; sur- 

 face smooth, with nearly obsolete lines of growth ; sides almost 

 parallel. 



