68 I. IJIMA : HEXACTINELLIDA. I. 



The meshes, whether perforate or interstitial, are nearly 

 quadratic but often somewhat elongated in the longitudinal 

 direction. They are usually largest in the middle region of the 

 body, where they may measure as much as 4 mm. by 6 mm. 

 (spec. J of the list given on p. 62). Towards either end of the 

 body they diminish in size down to say 2-3 mm. in length of 

 the sides. 



The numbers of the transverse and the longitudinal ridges 

 (which correspond to the main skeletal beams pursuing the same 

 direction) as counted on two specimens {D & J oï the list), both 

 of which had fully acquired mature form, were as follows : 



Spec. D. Spec. .7. 



Number of transverse beams 112 139 



Number of longitudinal beams at the upper 



end 73(?) 107(?), 



Ditto, at the middle 47 49 



Ditto, at the lower end 27 25 



In four more specimens — all macerated skeletons consisting 

 of fused spicules — I have found the number of longitudinal beams 

 at the lower extremity to be 22, 23, 23, and 28 respectively. It 

 then seems that we shall not be wide of the mark in stating 

 generally that the longitudinal beams in old individuals begin at 

 the lower end with a number somewhere between 22 and 28, and 

 that this number nearly doubles at the middle and triples or 

 quadruples at the upper end of the body. It goes without saying 

 that this multiplication is due to the splitting and divergence of 

 the beams in their course. It often happens, especially close to 

 the upper end, that the longitudinal beams are incompletely or 

 but slightly shifted asunder, making it impossible to count their 



