CONCHIFERA. 721 



GRUNDLER Naturforscher, n. 1774, pp. 82, 83. The arms have 

 in their axis a tendinous canal closed at the extremities, which, 

 according to OWEN, 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 Terebratula, 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. 



Lingula BRUGL, LAM. Shell subequivalve, flattened, oblong, 

 thin, gaping at both ends, affixed by a peduncle fleshy, cylindrical, 

 hollow internally. 



Sp. Lingula anatina LAM., BLAINV. PI. 51, fig. 3, GUERIN Iconoyr., Moll. 

 PL 36, fig. I ; 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. XL. fig. L. LINNAEUS named such an one 

 Patella unguis. The first account of two shells connected together was 

 given by CHEMNITZ (Naturforscher, xxn. 1787, pp. 2332, Tab. in.). 



Of late years a few other living species of this genus have been discovered. 

 Compare BRODERIP 1. 1. arid on the anatomy of Lingula, besides CUVIER 

 and OWEN, as cited above, also C. VOGT Neue Denkschriften der allg. 

 Schweizer Gesellschaft f. d. ges. Natunviss. vn. Neuchatel, 1845, mit ^ Taf. 



Fossil species also of this genus are found, especially in the Silurian 

 formation, also in the moun tain-lime. In the Muschel-kalk and bunter Sand- 

 stein Lingula tenidssima is found, BRONN Leth. geogn. Tab. xu. fig. 6 B. 



Orbicula Cuv., LAM. Shell inequi valve, orbicular. Affixed 

 valve plane, cloven in the disc ; superior valve conical. 



Sp. Orbicula Norwegica LAM., Patella anomala MUELL., Zool. Danic. Tab. 

 v., BLAINV. MalacoL PL 55, fig. 5 ; attached to rocks and shells in the 

 North Sea; Orbic. lamellosa BRODER., 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. SOWERBT Trans. Linn. Soc. xin. p. 472. 



VOL. f. 46 



