84 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 81 



remaining near the marginal parts of the oscuhim. The incurrent 

 apertures vary considerably in size, measuring 1 mm to 5 mm in 

 diameter, and sparsely scattered with small and large ones inter- 

 mingling. The excurrent ones are like the former in size and shape. 

 The wall is about 9 mm thick in the middle, becoming gradually 

 thinner toward the oscular margin, where it measures 1 mm. 



Spiculation. — The parenchymalia are mainlj^ slender diactins of 

 widely varying sizes, reaching 7 mm in length and 20/x in thickness 

 at the middle. They are sparsely distributed and are infrequently 

 present singly or forming small bundles. The gradually tapering 

 rays are provided with microspines at the end. The slenderer par- 

 enchymalia present no features worthy of special mention. 



The hypodermalia and hypogastralia are predominantly diactins, 

 which are much stronger and longer than those of the parenchyme, 

 measuring 6 mm in length and 30/a to 50/a in thickness at the center. 

 These spicules usually occur singly, rarely forming bundles, and are 

 more densely distributed than in the parenchyme layer. They are 

 nearly the same breadth throughout, with conically pointed, occa- 

 sionally distinctly circular, expanded ends, the surface of which is 

 usually microspined. Comitalia are slender diactins, smooth, but 

 with roughened conically pointed ends. The length may reach 3 

 mm or more and the thickness at the middle IS^u.. 



The dermalia are rather thick-rayed pentactins, the paratangen- 

 tial rays of which are strongly arched on the dermal plane. Occa- 

 sionally hexactins (fig. 10, a), stauractins. and tauractins are found. 

 In the pentactins, the paratangential, as measured from the central 

 point, is 90/A to lOO/n long; the thickness at the base averages 12ju. 

 The rays are very slightly narrowed outward ; the tip is rounded or 

 somewhat conically pointed. Their surface is thickly beset all over 

 with well-developed, erect, and conical, or tubercular, prickles, which 

 constitute one of the most striking characteristics of the species, as 

 ^it does of A. mlts'ukurii. The hexactins and stauractins need no 

 special mention. The quadrate meshes formed by apposed rays of 

 the dermalia measure 100/* to 120;it in length of sides. 



The gastralia are prominently stronger and larger hexactins 

 (fig. 10, l>) than those of the dermal layer, and are rarely pentactins. 

 The raj^s are somewhat tapering toward the ends; the prickles on 

 the surface are not so strongly and conspicuously developed as those 

 of the dermalia. The proximal ray is the longest of the rays, meas- 

 uring l'20jLi to 210/i, in lengtli while the distal ray measures 112;u, to 

 128/x. The paratangentials are nearly straight and measure 108/x, 

 to 132/x, ; the thickness at the base averages 10/*. The quadrate meshes 

 formed by the paratangentials of the gastralia usually measure 120/>t 

 in length of sides. 



