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capitate rays vary, in different spicules, very much in their 

 form and dimensions, some are very small, cylindrical and 

 blunted, others, at the point of junction with the shaft, are as 

 stout as the shaft itself and become gradually pointed, whilst 

 in other spicules the head rays are largely developed, fre- 

 quently accompanied by a diminution of the shaft, which in 

 the extreme forms is reduced to a small blunted process. 

 Neither are the rays themselves uniform, very often one is 

 longer or shorter than the others of the same spicule. Another 

 feature of these capitate rays is that one or all of them may 

 bifurcate and the divisions, like the simple rays, are often of un- 

 equal length. That this bifurcation of the capitate rays is 

 only a further development of the growth of each ray and 

 not characteristic of a particular form of spicule, is evident 

 by the numerous examples in this flint meal , in which a 

 gradual transition may be seen from specimens which have 

 all the rays simple, to those in which one, two, and finally all 

 three of the rays are bifurcated. 



For this form of spicule in which the shaft is very pro- 

 minent in relation to the head rays, as well as for those in 

 which the shaft has been reduced, but can yet be recognized 

 as distinct from the head rays, I propose to employ the term 

 trifid spicule, and where the rays are simple, to denominate 

 the spicule simple trifid^ and where bifurcate, compound 

 trifid.* 



The other main form of quadriaxial spicule has the four 

 divisions or arms more or less like each other, so that it is 

 not easy to determine which of them corresponds to the shaft 

 of the trifid spicule. In a very few instances one of the arms 

 of these spicules has been extended beyond the central point 

 so that a five rayed spicule results. The arms of these four 

 rayed spicules sometimes radiate from the centre at an equal 

 angle from each other, but in other examples one arm is at 

 a more or less open angle and occasionally nearly at a right angle 

 to the other three arms. A few of these spicules also have 



