56 
ZOOLOGT, 
Bracliiopoda were generally, and still are by some authors, 
considered to be mollusks, though aberrant in type. The 
shell of our common northern species, Terehrahdina sep- 
teiitrmialis (Fig. 61), which lives attached to rocks in fron\ 
ten to fifty or more fathoms north of Cape Cod, is in shape 
somewhat like an ancient Roman lamp, the upper 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 {Terebratulina) or largely {Lingula^ 
Fig. 62) of phosphate of lime. It is really the thickened 
Fig. 61.— Terebratvilina 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, with a limestone or partly chitinous, inequivalve, 
hinged or unhinged shell, enclosing the worm-like animal; 
with two spirally coiled arms provided with dense ciliated 
tentacles, and capable of reaching to or beyond the edge of 
the gaping shell; the alimentary canal has the mouth open- 
ingbetween the arms; there is an oesophagus, 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 oesophagus, and two lateral ventral widely 
separated threads. There are no eyes in the adult, but they 
are present in the young; auditory sacs are present in Lin- 
gula; There is no circulatory system. The germ passes 
through a morula and gastrula stage, becoming a segmented 
