5G PKOP. P. M. DUNCAN AND Mil. TV. P. SLADEN ON THE 
The curved edges of the inner extremity of the peristomial tube, 
as seen from below upwards, are not the terminations of the 
ambulacra aud iuterradia ; for when a section is made transversely 
through a test at the ambitus, and the chalk is cleared out from 
the actinal portion of the divided mass, plates are seen forming 
an internal oblique projection in the position of the perignathic 
girdle. 
The projection is continuous around and above the peristomial 
tube, and is a perignathic girdle of a very remarkable and unique 
kind. The girdle is well seen in a specimen at the British Museum 
No. 40341 (fig. 8) ; and it will be observed that the so-called 
Fig. 8. 
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ribs, ten in number, which pass over the inuer surface of the 
actinal interradial plates, commence at the outer edge of the 
interradial parts of the girdle. The girdle is rather low, and sur- 
rounds the peristomial opening in the form of a raised, oblique, 
broad, ridge-like ring. The upper surface of the girdle is free, 
and consists of flat or slightly irregular slanting surfaces, the 
slant being towards the peristome, ending all round aud out- 
wards in a continuous and wavy free edge. This edge h:is the 
parts which correspond with the ambulacra thin, less projecting 
than the other portions, and re-enteringly curved. The parts 
