LANUGONYCHIA FLABELLUM. 



105 



met, the diactines being particularly abundant. Judging l)y analogy I should 

 say that the surface, the skeleton of which consists chiefly of true hexactines, is 

 gastral, the other dermal. 



The hexactine and pentactine forms are orientated in such manner that 

 four of their rays extend paratangentially whilst one protrudes vertically out- 

 ward. The stauractines, triactines, diactines, and monactines are usually 

 extended wholly paratangentially. 



The rhabds are 4-20 mm. long and 5-140 n thick near the middle. Those 

 5-50 M thick are usually 4-7 mm. long. The slender ones are always distinctly 

 centrotyle, the tyle being 1-6 ^ thicker than the adjacent parts of the spicule. 

 In the stout rhabds the central tyle is only slightly developed, inconspicuous, 

 and often altogether absent. The axial cross is equally developed in the stout 

 non-centrotyle and the slender centrotyle rhabds. The smallest rhabds are 

 nearly cyUndrical and rounded at the ends. The rhabds 20^0 /i thick in the 

 middle taper gradually to 5-18 n towards the ends, which are usually unequally 

 stout and simply rounded off. The large, stout rhabds generally have blunt, 

 somewhat irregular, conic termini and are, just below the end, considerably 

 thinner than the small slender rhabds. The measurements of five rhabds, 

 tabulated below, indicate that these spicules are the more centrotyle and the 

 more cylindrical the smaller they are, and vice versa. 



RHABDS. 



The ends of the rhabds are, for a short distance, covered with small spines. 

 Apart from tliis these spicules are smooth. The .spiculation of the end-parts is 

 more conspicuous in the small than in the large rhabds. 



