450 Mr. H. J. Carter on the 



complete, as well as for the purpose of identification just men- 

 tioned, we will direct our attention for a few moments to this 

 part of the subject. 



Aphrocallistes Bocagei. 



Taking Aphrocallistes Bocagei first, as this is the simplest 

 form, it will be found that, besides the common large sexradiate 

 spicule on which the vitreous structure is based, there are seven 

 other kinds attendant upon it, all of which are more or less free 

 and unimplicated in the vitreous sarcode, viz. : — 



1. The staple, linear , fusiform spicule with inflated centre 

 and extremities, in which the former presents 2-4 tubercles 

 more or less developed opposite corresponding branches of the 

 sexradiate central canal ; extremities more or less pointed and 

 spined. 



2. A more delicate, linear, fusiform spicule, spined 

 throughout. The spines long and slender, supported on pro- 

 jections of the shaft resembling the bracket-steps of a flagstaff; 

 more or less closely inclined towards the shaft, and all in the 

 same direction — that is, not half one way and half the other, 

 beginning from the centre of the shaft and proceeding in oppo- 

 site directions, but from one end towards the other throughout. 

 As this is a very common form in the Hexactinellidas, and the 

 other kind also exists occasionally, viz. that in which the spines 

 are inclined towards either point beginning from the centre, it 

 is necessary to note the difference and give particular attention 

 to the form chiefly under consideration (PI. XV. fig. 8). 



3. A sexradiate spicule whose arms are more or less un- 

 equal in length — five being smooth at the commencement and 

 conically inflated and spined at the termination, and the sixth 

 spined, feather-like all round, the spines increasing in length 

 from the fixed to the free end. Sometimes, in an abnormal 

 state, more than one of the arms is thus spined (fig. 9). 



4. A scopuline spicule, consisting of a long shaft and four 

 rays. The rays more or less divergent, arising from a cor- 

 responding number of tubercles at the end of the shaft, and 

 terminating in conical heads surrounded with recurved spines. 

 The rays are microspined and the end of the shaft also. 

 Frequently the shaft presents a quadriform inflation just below 

 the giving off of the rays ; and sometimes the little tubercle 

 in the centre of the four rays, which is the end of the shaft, 

 is prolonged into a fifth ray (figs. 1 &,ld). 



5. A rosette with five-rayed arms, each ray straight or 

 slightly sigmoid, and all divergent and capitate, except the 

 central one, which is in a line with the arm ; head of the ray 

 convex and spined round the margin more or less deeply 



