ART. 12 HEXACTINELLID SPONGES OK ADA 109 



and the breadth 57 mm measured at the broadest part, which is 

 just above the middle of the entire stock. The smaller one is 20 mm 

 in height and 12 mm in breadth. The dermal surface is rough and 

 is covered with pentactinic pleuralia on the inferior parts of the 

 sponge body. The oscular margin is much injured, only a part 

 remains of one side and it seems not to flare out. The orifice is sub- 

 circular, with a thin edge. The incurrent canalar apertures are very 

 small, attaining a size of nearly 0.5 mm and becoming smaller toward 

 the upper region of the sponge; they are numerous and distributed 

 closely together. The excurrent canalar apertures are also small, 

 nearly the same size as those of the incurrent canalar apertures, 

 covered by the thin gastral layer. The thickness of the wall near 

 the basal region is 3 mm to 4 mm, which becomes thinner toward the 

 oscular edge. 



Spiculation. — Parenchymalia are long diactins, wdiolly smooth on 

 the center and roughened or microspined toward the ends, with 

 sharply pointed or conically pointed ends. The slenderer ones are 

 in bundles, and the thicker are isolated. 



Hypodermal oxypentactins with the paratangential rays are 

 paratropal, more or less curved, smooth, and provided with nearly 

 regularly distributed, sharply pointed thorns. 



Dermalia are rough pentactins, occasionally hexactins, or rarely 

 stauractins. The rays average 115)a long, measured from the center, 

 and 12;u, thick. They taper outward to a slight degree ; the ends are 

 rounded or conically pointed. The paratangential cross is usually 

 not convex on the outside and measures 220/1, to 240/x in length. 

 Seen surface on, the delicate dermal latticework presents irregular 

 meshes, though in places these show a tendency to assume a regular 

 quadrate arrangement, measuring 130/x in length of sides. The 

 hexactins and stauractins are of usual appearance and have nearly 

 the same length of ray, lOO/i to 150/* long. The latter spicules seem 

 to be more abundant than the former. 



The gastralia are chiefly hexactins (fig. 15, a). The rays are 

 similar to those of the dermalia; only they are usually of a much 

 greater dimension. The paratangentials are somewhat longer than 

 the distal ray, measuring 120/x to 135/t in length, though they are 

 much shorter than the proximal ray, which may attain a length of 

 ITO/A. The rays are lO/i thick at the base and taper somewhat 

 strongly outward to sharply or conically pointed ends. Except for 

 the central node, all surfaces of the rays are microspined, though 

 more sparsely proximally. 



Three varieties of oxyhexasters may be distinguished, designated 

 by letters A, B, and C. 



The first oxyhexaster, form A (fig. 15, e), occurs mostly in the 

 ectosome and occasionally intermixed with form C in the choano- 



