46 ZOOLOGY. 



Brachiopoda were generally, and still are by some authors, 

 considered to be niollusks, tliongh aberrant in type. The 

 shell of our common northern species, TcrehratuUna sep- 

 tentrionalis (Fig. 49), which lives attached to rocks in fronj 

 ten to fifty or more fathoms north of Cape Cod, is in shajie 

 somewhat like an ancient Roman lamp, the njiper and 

 larger valve being perforated at the base for the passage 

 through it of a peduncle by which the animal is attached 

 to rocks. The shell is secreted by the skin, and is com- 

 posed of carbonate {TereiratuKna) or largely (Lingida, 

 Fig. 50) of phosphate of lime. It is really the thickened 



Fig. 49 — Terebratulina or lamp-shell. Upper, and side view, natural size. 

 From Emerton, after Morse. 



skin of the animal, the so called mantle being the inner 

 portion of the skin. 



The Brachiopods may be briefly described as shelled 

 worms, witli a limestone or partly chitinous, inequivalve, 

 hinged or unhinged shell, enclosing the worm-like animal; 

 with two spirally coiled arms jirovided with dense ciliated 

 tentacles, and capable of reaching to or beyond the edge of 

 the gaping shell; the alimentary cnnal has the mouth open- 

 ingbetween the arms; there is an ojsophagus. a stomach with 

 a liver-mass on each side, and a short intestine ending in a 

 blind sac. The nervous system consists of a ganglion above 

 and beneath the cesopliagus, and two lateral ventral widely 

 separated threads. There are no eyes in tlie adult, )>nt they 

 are jiresent in the young; auditory sacs are iireseut in Lin- 

 gula. There is no circulatory system. I'he germ passes 

 through a morula and gastrula stage, becoming a segmented 



