Arathi 
CONCHIFERA. 721 
GrunpDLeR Naturforscher, u. 1774, pp. 82, 83. The arms have 
in their axis a tendinous canal closed at the extremities, which, 
according to Owsry, is filled internally with a fluid. Muscular fibres 
which surround the canal force, in his opinion, this fluid to the outer 
extremity, and thus cause the arms to unfold. 
In the third place the Brachiopoda are characterised by the 
absence of an elastic ligament, which in the Lamellibranchiates 
exists at the hinge of the shells and works antagonistically with the 
adductor muscles. Thus the shell is opened here by the arms, 
or also, in Zerebratula, by the elasticity of a composite apparatus of 
thin calcareous loops which are attached within, to the surface of 
the lesser imperforate shell. Hence arises a more complex dispo- 
sition of the muscular system, which is formed of different oblique 
bundles in place of the single or double adductor muscle found in 
the Lamellibranchiates. 
I. Shell hingeless. 
LTingula Brua., Lam. Shell subequivalve, flattened, oblong, 
thin, gaping at both ends, affixed by a peduncle fleshy, cylindrical, 
hollow internally. 
Sp. Lingula anatina Lam., Buatnv. Pl. 51, fig. 3, Guérin Iconogr., Moll. 
Pl. 36, fig. 1; from the East Indian Ocean. Formerly detached shells 
alone of this animal were known; such a single shell is figured by Rum- 
PHIUS Amb. Rariteitk. Tab. xu. fig. L. LinNavUS named such an one 
Patella unguis. The first account of two shells connected together was 
given by CuEemnitz (Natwrforscher, XX11. 1787, pp. 23—32, Tab. 1.). 
Of late years a few other living species of this genus have been discovered. 
Compare Broperip 1. 1. and on the anatomy of Lingula, besides CUVIER 
and OWEN, as cited above, also C. Voer Neue Denkschriften der allg. 
Schweizer Gesellschaft f. d. ges. Naturwiss. vi. Neuchatel, 1845, mit 2 Taf. 
Fossil species also of this genus are found, especially in the Silurian 
formation, also in the mountain-lime. In the Muschel-kalk and bunter Sand- 
stein Lingula tenuissima is found, Bronn Leth. geogn. Tab. x11. fig. 6B. 
Orbicula Cuy., LAM. Shell inequivalve, orbicular. Affixed 
valve plane, cloven in the disc; superior valve conical. 
Sp. Orbicula Norwegica Lam., Patella anomala Murtu., Zool. Danic. Tab. 
v., Buainv. Malacol. Pl. 55, fig. 5; attached to rocks and shells in the 
North Sea ;—Orbic. lamellosa BroprEr., Trans. Zool. Soc. Tab. 23, fig. 2, on 
the coast of Peru, &c. 
Note.—Genus Discina Lam. to be abolished, not being distinct from 
Orbicula ; see G. B, SowErBy Trans. Linn. Soc. X11. p. 472. 
VOU.I. 46 
