INVERTEBRATE PALAEONTOLOGY. 7 



MOLLUSCA. 



BRACHIOPODA. 



LYOPOMATA. 



LINGULIDiE. 



Genus LINGXJLA, Bruguiere. 



Synon.-Lingula, Brug. (1792), Encyc. M6tb., tab. 250.— Cnvier (1798), Tabl. elem., 435; and (1802), Ann. 

 du Mu8., I, 69.— Lamarck (1799), Prour., 89; and (1801), Syst. An., 140.— Roissy (1805), 

 Moll., VI, 468.— Schw. (1820), Nat., 690.— Desh. (1830), Man., 257, &c. 

 Pharetra, Bolten (1798), Mus. Bolt., sec. ed., Ill (not Hubn., 1816). 



Etym.—Lingula, a little tongue. 

 Type. — Lingula anatina. Lam. 



Shell thin, oblong or more or less oval, depressed, gaping at the beaks, 

 subequivalve, rounded or subtruncate anteriorly, and more or less pointed at 

 the umbones ; substance largely phosphatic in composition, and consisting of 

 alternate corneous and testaceous laminae, the former of which is fibrous, 

 and the latter tabular; valves both moderately convex or compressed, and held 

 together by the action of muscles ; beak of ventral valve more prominent 

 and pointed than the other; surface smooth, or marked by concentric striae, 

 sometimes crossed by radiating lines, covered by a thin epidermis ; interior 

 without projecting laminae or other processes. Peduncle long, cylindrical, 

 fleshy, and flexible, being supplied with muscles, by means of which the 

 animal can bend it about when detached, or move itself and the shell when 

 attached to some foreign body at its extremity. 



The interior of the valves, in the typical forms of this genus, is largely 

 occupied posteriorly by the marks of the visceral sack and the scars of the 

 complex muscular system. In the dorsal or shorter valve, this visceral area 

 has a somewhat rhombic or suboval form, and in the ventral valve its outline 

 is ovate-cordate, or more or less flabelliform. The area thus designated is 

 usually slightly thicker in both valves than other parts of the shell, especially 

 in old examples, so as to leave a faint impression on internal casts of fossil 

 species. 



Twelve muscular scars have been observed in the interior of the dorsal 

 valve,and thirteen in the ventral. The scar of the peduncular muscle is situated 



