SILICIOUS AND HORNY SPONGES WILSON. 433 



not in brushes, but are scattered or in loose groups of a few; they 

 lie along with the bunches of projecting skeletal spicules and between 

 them. There is a difference, but only one of degree, between the two 

 surfaces of the sponge. On the oscular surface, the ectosomal spi- 

 cules are more abundant and they seem to average a greater length 

 than on the pore surface. 



The skeletal spicule (pi. 49, fig. 5, a) is a spinose style, slightly 

 curved, 280-350 by 18-20 ^. The spines are mere prickles scattered 

 along the shaft in some abundance, thickly set at the extreme basal 

 end. 



The ectosomal megascleres are variable, but always smooth and 

 slender; 150-280 by 4-5 \x.. The common type (pi. 49, fig. 5, b) 

 is a tylostrongyle in which the basal end, which is the innermost 

 in a radially placed spicule, is slightly tylote. Sometimes (rarely) 

 both ends of the spicule are slightly tylote, but even then one end 

 (the inner) is larger than the other. Sometimes, not often, neither 

 end is thickened, the spicule being a strongyle. On the oscular 

 surface of the sponge it not infrequently happens that the outer 

 end is pointed, the spicule becoming a tylostyle. As said above, 

 the spicules seem to average a larger size on the oscular surface 

 than on the pore surface. On the former, the common range in 

 length is 160-280 \i (15 spicules measured). On the latter, the 

 common range in length is 150-200 [J. (15 spicules measured). 



The isochelas (pi. 49, fig. 5, d) are 14-20 \i long. They are 

 abundant in the interior and in the dermal membrane of both sur- 

 faces. I have examined them with an immersion objective (Zeiss) 

 in balsam and water. They are very transparent, but I find them 

 to be chelae palmatae and not chelae arcuatae — that is, the axis 

 is not greatly curved, nor is the ala separated below from the axis 

 b.y a conspicuous notch, and the tooth is broad. 



Toxas (pi. 49, fig. 5, c) are abundant close to the dermal mem- 

 brane and in the interior. The spicule is much bent at the middle 

 and the ends sharp; 150-350 (jl long, 2-3 jjl thick. Smaller sizes, 

 young stages, are common. 



Holotype.— Oat. No. 21272, U.S.N.M. 



Genus COELOSPHAERA Wyville Thomson (1873). 



Coelosphaera Wyville Thomson, 1873, p. 484. — Dendy, 1921&, p. 102. 

 Histoderma Carter, 1874, p. 220. — Topsent, 1894c, p. 10. — Dendy, 1905, 

 p. 166.— Part, Lundbeck, 1910, p. 7. 



Body typically spheroidal and phloeodictyine in appearance, with 



a hard dermal layer made up of closely packed tangentially placed 



megascleres, and with fistular processes. Typically the megascleres 



are tylotes, fusiform or subfusiform, varying to strongyles of similar 



81709—25 12 



