377 
Fig. 2. 
Fig. 3. 
Fig. 4. 
Fig. 5. 
Fig. 6 
Fig. 7. 
Fig. 8, 
Fig. 9. 
THE ECHINUS, OH SEA-URCHIN. 
Inside of the shell of an echinus to show — L , Aristotle’s lantern ; 
an, an auricula ; a, ambulacra : i, interamhulacra. 
Oral pole of an echinus, showing the apices of the five teeth pro- 
truding from the mouth. 
Apical pole of an echinus — a, ambulacra ; i, interambulacra ; g, one 
of the five genital plates; in, madreporic tubercle, and modified 
genital plate ; o, ocular plates. 
Parts which compose Aristotle’s lantern ; al, alveoli enclosing t, 
teeth ; r , rotulce ; d f radii. 
Cucumaria , one of the Holothuridea. 
TJraster , one of the Asteridea, showing the oral surface and the 
ambulacra in grooves in the so-called arm3. 
, One of the Ophiuridca : the oral surface. 
Comatula , one of the Crinoidea : side view. The mouth turned 
downwards ; c , cirri surrounding the base of the calix. 
