381 



It is proposed to call these the radial stolons ; they form continuous lines 

 radiating in all directions away from the nucleus. The other two stolons 

 of each tube project at right angles to the direction of the radial stolons ; 

 they form circles round the nucleus, and may therefore be called the 

 cyclical stolons. The connection of all these different parts may be better 

 understood by studying the following figures. 



Fig. 354. 



Fig. 355. 



Fig. 356. 



Fig. 354. A small portion of R. occidentalis showing the tubes. 



Fig. 355. A part of the lower side of the same species showing the nucleus and ector- 

 hin. 



Fig. 356. A fragment of the same, showing the endorhin, the pores at the angles of 

 the plates, and the nucleus, which, on this side, is usually deeply con- 

 cave. 



At the lower side of fig. 354, is shown the ectorhin and the apertures 

 in the hollow stolons, broken off in the specimen. The apertures are 

 slightly enlarged in the figure. In fig. 355, the usual aspect of the cen- 

 tral portion of the lower side of this species is given. It will be seen that 

 the greater number of the plates are not truly rhomboidal, but approach 

 the form of a spherical triangle with two of the sides concave. This form 

 of the plates frequently occurs. The convex side of such plates is always 

 outwards towards the periphery of the fossil, and the acute angle formed 

 by the two concave sides always directed towards the nucleus. This 

 shows that the consolidation of the plates commenced at the nucleus and 

 gradually extended outwards. In many specimens the plates are all per- 

 fectly rhomboidal, and in such they may have solidified simultaneously all 

 over the body. One corner of the specimen at a is represented as denuded 

 of the ectorhin, showing the various markings beneath, which will be here- 



