OF THE TEST OF THE TEMNOPLEUEIDiE. 353 



and passes from close to the outside of the test to the inner part 

 of the edge. 



The edge of the iuterradial plates in contact with the pori- 

 ferous plates of the ambulacrum has two rows of large sockets 

 parallel with the surface of the test. There are no other pits to 

 be seen there, except those at the ends of the horizontal sutural 

 margins between the interradial plates. 



A more confused knob-and-socket arrangement is seen on the 

 median edge of the ambulacral plates than on the corresponding 

 edgeof theinterradials. But there is a general resemblance. The 

 deepest pits are near the peristome ; and on either side of them, 

 on the edge of the plate, are confused nodules and depressions 

 rather than well-defined knobs and sockets. Moreover, the run- 

 ning together of the knobs and sockets, respectively, in lines 

 occurs, and the solitary lines passing from without inwards arc 

 visible. The deepest pits near the peristome, four or five in 

 number, hold sphseridia of considerable dimensions. 



The edge of the poriferous plates in contact with the inter- 

 radium has two large rows of knobs ; and here and there they 

 run together to form rounded-off wedges. This arrangement is 

 much more simple than in the adult form ; and is seen less dis- 

 tinctly towards the apical part of the ambulacrum. 



Pinally, the actinal and abactinal edges of the interradial and 

 ambulacral plateshave a small number of knobs and sockets. 



V. The Pits and Sutttres of Salmacis bicolor and 

 Amblypueustes ovum. 



Salmacis hicolor.—The pits in this species are small externally ; 

 but they pass down far towards the inner part of the test, as cylin- 

 drical tubes (Plate YIII. figs. 15-17). A very considerable 

 development of knobs and sockets is found on the median inter- 

 ambulacral and ambulacral plate-edges, and lines of more or less 

 continuous depression and elevation also occur. The suturing is 

 slighter than in the otber species, but tbe knobs are often larger. 

 The same kind of suture is found between the interradial plates 

 and the ambulacral poriferous plates as in the species already 

 mentioned. But the knob-and-socket suturing of the actinal and 

 abactinal horizontal edges of the plates, coronal and ambulacral, 

 although it exists, is slight and often difficult to see. Here and 

 there it is replaced by linear elevated tracts and corresponding 

 long depressions. 



