170 ZOOLOGY 
1100 species have been described from Devonian rocks, Since 
this epoch they have dwindled, and at the present day not 
more than about 100 species exist. 
Argiope (Cistella) neapolitana is a small Brachiopod found 
attached by a peduncle to pieces of rock at a depth of about 70 
metres in the Mediterranean. The dorsal and ventral shells 
entirely cover the body except the peduncle, which projects 
through a “beak” formed by the ventral or larger shell. The 
Fic. 107.—A longitudinal vertical median 
section through Argiope neapolitand. 
Ventral shell. 
Canal containing blood-vessel. 
Sub-oesophageal nerve ganglion. 
Pow Por 
Mouth. 
OO 
Stomach. 
2 
Peduncele. 
“I 
Plexus of blood-vessels. 
Median crest on dorsal shell. 
i 
Organic membrane which has separated 
from shell during the process of de- 
calcification. 
dorsal shell is rather the smaller; both are of a brownish hue 
with small white spots. The body of the Avgiope lies almost 
entirely in the dorsal shell (Fig. 107), and is supported by 
certain ridges which this shell bears on its inner surface. The 
