56 PROF. p. M. DUNCATT AT^D ME. W. 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 and interradia ; 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. 



ribs, ten in number, which pass over the inner 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 J^e girdle is free, 

 and consists of flat or slightly irregular slanting surfaces, the 

 slant being towards the peristome, ending all round and out- 

 wards in a continuous and wavy free edge. This edge has the 

 parts which correspond with the ambulacra thin, less projecting 

 than" the other portions, and re-enteringly curved. The parts 



