LINGULA TEREBRATULA. 



69 



Fig. 111. 



TERKDRATULA. 



and a bivalve shell ; they have no foot, but 

 in place of it, two fleshy arms furnished 

 with filaments, and susceptible of being un- 

 folded externally, or drawn within the shell 

 by folding spirally (fg. Ill, a); their 

 branchiae are not distinct from the mantle, 

 and the mass formed by their viscera is very 

 small. They are unprovided with organs of 

 locomotion, and live attached to submarine 

 bodies. 



The principal genera composing this 

 group, are the Lingula, Terebratula, and 

 Orbicula. 



23. The LINGTJL.E are provided with a long fleshy peduncle, 

 one extremity of which is generally attached to the rocks these 

 animals ordinarily inhabit, and the other is furnished with two 

 oblong, flattened valves. Their arms, which are inserted in the 

 sides of the mouth, are very long ; and the branchial vessels 

 are distributed on the internal face of the mantle, and there form 

 on each side a series of small parallel folds. They are found in 

 the Asiatic Seas. 



24. The TEREBRATUL^E have two 

 unequal valves joined by a hinge, 

 and one of them (fig, 112) has a 

 hole through its summit for the pas- 

 sage of a fleshy peduncle, by means 

 of which the animal attaches itself. 

 Their branchiae are less distinct than 

 in the LinguIcC, and consist simply of 

 a vascular net-work spread over the 

 internal face of the mantle; but 

 their muscular system is more de- 

 veloped, and there is found in the 

 interior of the shell a small solid 

 frame (fg. 113), the structure of 

 which is sometimes very compli- 

 cated ; its chief uses are to afford 

 attachment to muscles, and to as- 

 sist in separating the valves. Some 

 living Terebratulse are found in 

 the South Seas ; but-' they abound 

 most in the fossil state; and are Fig. 113. TEREBRATULA. 



23. What are the characters of the genus Lin'gula ? (Lingula, Latin, a 

 latchet, or tongue of a shoe.) 



24. What are the characters of the Terebra'tulu ? (TerebratuJa. from th 

 Latin terebro, J bore.) 



8* 2Y 



Fig. 1 12. TEREBRATULA. 



