54 PKOCEEDINGS OF THE NATIONAL MUSEUM yol. 81 



Transitional scopular forms, connecting the smallest one to the 

 largest, here described, are quite frequent. Scopulae with fewer than 

 four branches are not found in intermedia. 



Uncinates, varying in length and thickness, quite frequently occur 

 close to the dictyonal honeycomb. They are arranged perpendicu- 

 larly to the dermal and mostly obliquely to the gastral surfaces and 

 usually reach only to the inner two-thirds of the whole thickness of 

 the body wall. The outer half of the spicule, nearer the dermal sur- 

 face, is always slightly thicker than the inner half, nearer the inner 

 regions of the parenchyme. The inner half tapers quite gradually 

 to the pointed end. The weak barbs around the shaft are not so 

 numerous. 



Of the spicules irregularly scattered throughout the parenchyme, I , 

 will first describe those simple hexactins that measure 140/x, to 160/* 

 in axial length and seem to play so important a part in the growth 

 of the dictyonal network. Their rays are fairly stout, straight, grad- 

 ually tapered, bluntly pointed, and irregularly covered with small, 

 more or less numerous tubercles. 



The peculiar oxyhexasters are scattered abundantly in the hypo- 

 gastral regions and are not found in the parenchyme ov in the der- 

 mal regions. They measure 24/i, to ^Sjx in diameter and have stout 

 principals 3/* broad near the base, being somewhat thicker toward 

 the distal end, from which numerous outwardly curved terminals 

 arise. These terminals vary in number from 10 to 13 on each prin- 

 cipal and are very short, about half as long as the principals. ^ 



Much more peculiar and worthy of interest are the hexactins, 

 hemihexactins, oxyhexasters, and onychasters, irregularly scattered 

 in varying numbers through the parenchyme. They are subject to 

 considerable variation ; their shape and size vary in different regions 

 of the same individual. They are frequently found in the same 

 place intermixing with one another. Four kinds of intermediary 

 parenchymalia, except the onychaster, are to be distinguished: 

 Stout-rayed microxyhexactins, microhexactinic and microhemi- 

 hexactinic forms, the rays of which show a tendency to bifurcation 

 so that they pass into oxyhexasters. 



The regular oxyhexasters with six equal main rays, which are 

 nearly the same thickness as the terminals, form right angles with 

 one another. They are terminally crowned with groups of 3 or 4 

 nearly straight branch rays of uniform thickness, shape, number, and 

 degree of divergence. The main rays, measuring 8/a at the base, 

 are generally short. The spicules usually have a diameter of not 

 more than 80/^. 



The microhexactins and hemihexactins have more or less the same 

 features, measuring SO/x to lOO/i in diameter. Their rays are strong 



