384 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Family STELLETID£ Sollas. 
Megascleres are oxeas and orthotrisenes, or plagiotrisenes, or dichotrkenes, frequently with ana- 
trisenes in addition. Microscleres include euasters, but never spirasters nor sterrasters. 
Genus PILOCHROTA Sollas (1886, 1888). 
“Oscules usually distinct. Pores in sieves leading into radial incurrent canals, which are not 
constricted on passing through the fibrous layer of the cortex. Ectosome differentiated to form a 
cortex, which usually consists of a middle collenchymatous layer, an outer thin fibrous layer, and an 
inner thicker fibrous layer.” There is but one form of aster, and this is a chiaster. 
Pilochrota variabilis, n. sp. 
Station 6079, two specimens; station 6090, three specimens; station ?, ten specimens. 
The sponges here described resemble several of Sollas’s species (P. hxckeli, P. pachydermala. P. 
purpurea , P. lendenfeldi), but the limitations laid down in Sollas’s descriptions (1888) make it 
impossible to refer my specimens to any of these species. 
Body spheroidal, often flattened. One specimen attached by its under surface obliquely to coral; 
the others free, many with foreign particles adhering to surface. Younger forms occasionally found 
with short (2 mm. or less in length) slender rhizoidson undersurface; such rhizoids being prolongations 
of soft tissue almost without megascleres. Color in alcohol whitish or purplish-brown. The larger 
specimens measure mostly 20 to 25 mm. in diameter; the smallest, apparently young forms, 5 to 7 mm. 
in diameter. 
In several of the larger specimens a single large osculum, 2 to 3 mm. diameter, is present, leading 
into a deep cloaca, on the inner wall of which the apertures of excurrent canals may be seen. Such an 
osculum may be situated in center of upper surface or nearer one side, then opening obliquely. In 
the attached specimen one such osculum is present on the side, low down, below the margin, while 
two other very small oscula, appearing as apertures in smooth membranous areas, are similarly situated. 
In one of the large specimens there are no oscula, but several smooth membranous areas on the surface. 
In another of the larger specimens a single small osculum is present in the center of a similar smooth 
membranous area. Most of the young (small) forms are without oscula, but in two cases a very small 
osculum is situated in center of upper surface. All oscula are surrounded by a smooth membranous 
border, narrow in the case of the larger ones. Appearances indicate that oscula may be opened and 
closed. 
Pores of variable size, but easily distinguishable with lens, lying in meshes of the network formed 
by cladi of the cortical orthotrisenes. Surface as seen with lens may be practically smooth and 
obviously porous, or punctate with minute elevations. Such elevations may be enlarged, appearing as 
areas of rounded polygonal shape, with pores in channels between — this appearance more obvious to 
eye than when sponge is examined with lens or objective, since the elevated areas themselves are 
porous. 
Cortex in the larger specimens about 700 p, in the younger forms only 500 p thick; fibrous with 
abundant densely granular cells, often in groups, in the outer half. Numerous subdermal cavities in 
the deeper portion of cortex form a conspicuous layer. These are connected with short, wide (some- 
times rounded) canals, which pass outward, branching near surface (often bifurcating), each branch 
terminating in a pore. 
Skeleton. — Megascleres. (1) Orthotrisene; rhabdome, tapering to a fine often whiplash-like end, 
1,350 to 1,700 p by 12 to 24 p ; cladi 100 to 250 p (increasing with length of rhabdome), slightly curved 
outward, then straightening or recurved near tip; center of cladome depressed. (2) Very slender 
orthotriaenes of variable size, probably young stages of the preceding, the cladi directed slightly 
forward so as to give to the spicule the plagiotrisene character; rhabdome tapering to fine long point. 
A common size has a rhabdome about 500 by 4 p, cladi 20 to 24 p. (3) Anatrisene with depressed 
apex, rhabdome tapering to point, 1,530 to 2,210 p by 20 to 24 p; cladi stout, tapering to sharp point, 
with length 44 to 84 /(, and sagitta 20 to 80 p, the sagitta increasing with the length of cladus, as 
does length of cladus with that of rhabdome. Cladome is thus comparatively shallow or quite deep. 
(4) Oxea smooth, tapering to sharp points, 1,020 to 1,600 p by 12 to 16 p, with much smaller forms 
of same spicule. (5) Ectosomal oxeas slightly curved, 168 to 200 p by 6 to 8 p. Such spicules occur 
scattered very sparsely through outer part of cortex; arranged vertically to surface and slightly project- 
