or THE TEST OF THE TEMNOl'LEUKIDiE. 351 



cata. The tentaculiferous plates, or the poriferous parts of the 

 ambulacra! plates, have kuobs and sockets arranged like those of 

 the main plate. 



On examining the edges of the interradial plates along the 

 median line the succession of pits is very distinct. They enlarge, 

 as has been stated already, slightly at their inner end in the vertical 

 direction, and reach inwards very close to the inner margui of the 

 edge. On either side of a pit, that is to say actinally and abacti- 

 nally in vertical succession, there is a curved process passing from 

 the inner part of the edge outwards, and then bending close to the 

 outer part of the edge towards the angle of the plate (Plate YIII. 

 fig. 12). These jn-ocesses, two to each plate, enclose a space ; and 

 one of them has one series of sockets, and the other one series of 

 knobs on it. The space is shallow and oblique, and is part of a pit. 

 On the inner part of the edge, below the space and the end of the 

 pit, there are groups of minute knobs and sockets. On the corre- 

 spondiug edge of the contiguous plate the same structures are 

 found ; but the position of the knobs and sockets is reversed, and 

 tbere is a slight projection which fits partly into the space. The 

 suturing is by the reception of the knobs by the sockets of the 

 approximated plate-edges. 



A similar arrangement occurs on the median edges of the plates 

 of the ambulacra! area ; but there is more variation in the extent 

 of the processes with knobs and sockets. 



In parts of the test where the pits are unusually large, there is 

 more than one series of processes, and a set of knobs and sockets 

 bound the space or projection, as tbe case may be. On the other 

 hand, near the peristome, where the pits are small, cylindrical, 

 and yet pass far inwards, the suturing is by nearly straiglit 

 lines of pits and sockets, Avhich are parallel with the pits and are 

 small. 



The junction of the outer edge of the interradial plate with the 

 poriferous plates of the ambulacrum is complicated by the presence 

 of the pits at the end of the horizontal marginal grooves (actinal 

 and abactiual), and by occasional pits at the junction of the 

 sutural lines of the small plates with the interradial. But the 

 suturing is by two to four processes, separated or not by pits, 

 and passing from the inner part of the edge of the plate to the 

 outer, just below the surface. 



The processes consist of two laminte of the reticulate tissue of 

 tlic test ; and between them are sockets in a series, or thev mav 



