352 :&EOF. 1". M. 1)11170 AN" ON THE MOEPHOLOGt 



run together and form linear depressions. The inner part of the 

 edge internal to the base of the processes is crowded with sockets 

 (Plate yill. fig. 13). 



PinaUj, the edge of the poriferous plates in contact with the 

 interradial is marked by series of knobs which fit into the sockets 

 in the corresponding interradial edge (Plate VIII. fig. 14). 



The plates of the apical disk do not join the coronal and ambu- 

 lacral plates by any knob-and-socket suture, but by a slight over- 

 lapping. 



It is perfectly evident that the union of the edges of the plates 

 of Temnopleurus toreumaticus and of Salmacis sulcata only difter 

 in matters of slight detail. In both there is a reversal of the 

 arrangement seen in tlie interradial area iu the ambulacral ; and 

 in both the poriferous plates have knobs and join the interradial 

 plates which are socketed. 



Young Forms of Tlem.wo'^lQuvws, toreumaticus. — Several specimens 

 of from ^ to ^inch in diameter were examined. There are round, 

 widely open shallow pits, the bottom of which can be seen from 

 the surface of the test above the ambitus in both areas, and the 

 marginal sutural grooving is slight. At the ambitus in some, 

 but not in all, the pits and grooves diminish in size, and are 

 often very small ; and below the ambitus, in all, the pits of the 

 ambulacral area are not so large as they are near the apex, and 

 those of the iuterradials are very minute. 



The edges of the interradial plates, along the vertical median line, 

 show that the pits barely pass within the test near the peristomej 

 and that they are deeper near the apical system ; but they do 

 not excavate the point of the angle of the plates. Where largest, 

 they do not pass inwards more than in Amllypneustes. In fact, 

 the flask-shape is not seen. 



The suturing is different to that in the adult form j and it con^ 

 sists, v/here the pit is very insignificant, of well-developed rows 

 of knobs, parallel with the outside of the test, or slightly irregular 

 in their distribution, and of sockets arranged in similar order. 

 The knobs are on one side of the pit and the sockets on the 

 other ; and they correspond with sockets and knobs on the op- 

 posed plates. Where the pits are larger and the sutural marginal 

 groove is more pronounced, the knobs and sockets are in arcs, 

 and frequently there are lines of knobs run together to form a 

 linear elevation ; and there are corresponding lines of depression. 

 Here and there one of these lines has a distinctly inward track, 



