Lamarck's Genera of Shells. 51 



scarcely perceptible, whence Mailer supposed it to be an uni- 

 valve shell, and referred it to the patellae. 



One Species. Orbicula Norvecjica *. (Patella anomala. Mull.) 

 Upper valve compressed, conical ; summit pointed, inclining on 

 one side towards the margin. North Sea. PI. II. Fig. 103. 

 2. Terebratula f. 



Shell inequivalve, regular, subtriangular, attached to marine 

 substances by a short tendinous pedicle. Beak of the larger 

 valve promment, often curved, perforated at the summit by a 

 round hole, or a notch. Hinge with two teeth ; two almost 

 osseous, slender, elevated, forked, and variously ramified 

 branches, spring from the interior disk of the smaller valve, and 

 serve as a support for the animal. 



The terebratulfe appear to be sea-shells, of wliich some recent 

 species are known, but the greater number are fossil. The hole 

 in the beak of the largest valve serves for the insertion of the 

 fleshy tendinous pedicle, by which the shell is fixed to marine 

 substances. The hinge is formed of two teeth, belonging to 

 the large valve, which fit into the pits of the lesser. 



The animal of tlig terebratula is nearly allied to that of the 

 lingula ; like it, it has two opposite, elongated arms, fringed, 

 or ciliated on one side, which it protrudes at pleasure beyond 

 the shell; when it returns them, they form a double fold from 

 bottom to top, their extremity only being curved, or rolled in a 

 spiral form. 



The species are divided into recent and fossil, and the former 

 subdivided into (1) shells smooth, without longitudinal stris, 

 or furrows, 5 species, and (2) those longitudinally furrowed, 

 7 species. The fossil species are also similarly subdivided. 

 Type. Terebratula vitreaX- (Anomia vitrea. Gmel.) 



Shell ovate, ventricose, glassy, very thin, smooth ; larger 

 beak prominent : perforation small. Mediterranean. In all 

 12 recent species, and 47 fossil. PI. 11. Fig. 104. 

 3. Lingula§. 



Shell subequivalve, flattened, oblong-oval, truncated at the 



Norwegian. t Ttrffcratujf, piVceJ, in allusion to the perforation of the 



larger valve. I GUtttsy. ^ A little tongue. 



E 2 



