BRACHIOPODA. 273 



LINGULA, Bruguieres. 



Two equal, flat, oblong valves, the summits of which are at the extremity of 



one of the narrow sides, gaping at the 

 other end, and attached between the 

 ' two summits to a fleshy pedicle, which 

 suspends them to the rocks ; the arms become spirally convoluted previously to 

 entering the shell. It appears that the branchiae consist of small leaflets, 

 disposed around the internal face of each lobe of the mantle. 



But a single species, Lingula anatina, Cuv., is known. It inhabits the 

 Indian Ocean, and has thin, horny, and greenish valves. 



TEREBRATULA, Bruguieres. 



Two unequal valves united by a hinge; the summit of one, more salient than 

 the other, is perforated to permit the passage of a fleshy pedicle which attaches 

 the shell to rocks, madrepores, other shells, &c. Internally, a small bony piece 

 of frame- work is observed, that is sometimes very complex, composed of two 

 branches which articulate with the unperforated valve, and that support two 

 arms edged all round with a long, close fringe, between which, on the side 

 next to the large valve, is a third, simply membranous and much longer ap- 

 pendage, usually spirally convoluted, and edged, like the arms, with a fine 

 and close fringe. The mouth is a small vertical fissure, between these three 

 large appendages. The principal part of the body, situated near the hinge, 

 contains the numerous muscles which reach from one valve to the other, and 

 between them are the viscera, which occupy but little space. 



Numberless Terebratulae are found, fossil or petrefied, in certain secondary 

 strata of ancient formations. The living species are less numerous. 



The shell of some is transversely broader or longer, in a direction perpen- 

 dicular to the hinge, with an entire or emarginated contour, with two or several 

 lobes ; some of them are even triangular ; the surface is smooth, sulcated in 

 radii, or veined; they are thick or thin, and even transparent. In several of 

 them, in lieu of the hole in the summit of the thin valve, there is a notch, 

 and this notch is sometimes partly formed by two accessory pieces, &c. It is 

 probable that when better known their animals will present generic differences. 

 Already in the 



SPIRIFER, Sowerby, 



Two large cones have been recognised, formed of a spiral thread, which 

 appear to have supported the animal In 



THJECIDEA, Def. } 



The pedicle seems to have been incorporated with the small valve. 



ORBICULA, Cuvier. 



The Orbicuke have two unequal valves, one of which, that is round and 

 conical when viewed by itself, resembles the shell of a Patella ; the other is 



T 



