BULLETIN OE THE UNITED STATES FISH COMMISSION. 
396 
Skeleton .- — Spicules: (1) Style slightly curved and smooth, 240 by 8 //, the chief spicule. (2) Tylote 
220 by 4 p, with slightly enlarged heads, which are minutely spined, sometimes only very slightly 
so spined or not at all. (3) The rhaphides are oxeas from 200 by 2 p down through successive sizes 
to spicules only 40 p long. The large forms, about 200 p long, are the more common. In these one 
end is often less slender and tapering than the other, and a most minute roughening of the surface 
can be made out. The spicules ai - e scattered irregularly through body, though there are ill-defined 
polyserial tracts (largely made up of styles), some of which extend vertically to the surface; also 
brushes of tylotes supporting the dermal membrane. Where several of the styles intersect they are 
cemented together by a small amount of spongin, and thus a vague, and quite irregular reticulum is 
formed. 
Schmidt (1870, p. 43) has shown how extremely variable is the habitus of the widely-spread 
sponges possessing the spicules mentioned above, and declines to erect new species for the West 
Indian forms. 
Family DESMACID0NID7E Ridley & Bendy. 
“Megasclera of various forms, usually monactinal. Microsclera always present and always includ- 
ing chelae.” 
Subfamily ECTYONIN® R. & D. 
“Skeleton fiber echinated by laterally projecting spicules.” 
Genus MICROCIONA Bowerbank (Topsent emend. 1894). 
Incrusting sponges. Skeleton a basal plate bearing short, upright plumose columns. Megascleres 
monactinal, smooth and spined. Microscleres: isochelae, often accompanied by toxas, sometimes by 
sigmas. 
Microciona spinosa, n. sp. 
Station 6079, two specimens. 
Sponge is a thin, firm incrustation covering a conglomerate mass of branched millepore coral and 
small lamellibraneh shells. Total size of mass in one specimen 110 by 60 mm., in other 80 by 50 mm. 
Incrustation 0.5 mm. or less in thickness, and closely beset with spine-like radiating processes, fre- 
quently divided terminally, 1 to 2 mm. high and about 600 ft thick. (Where incrustation is apparently 
young the body is particularly thin and the radiating processes are just beginning to develop.) From 
ends and sides of the processes, and from the general surface, stout styli project 200 p or more beyond 
dermal membrane. The styli, which are the echinating spicules of the horny skeleton, may be in small 
tufts or distributed singly. Color a dull pink. 
Skeleton. — Horny skeleton consists of an extremely thin basal membrane, bearing stout radiating 
columns, latter forming the support of the spine-like processes. In the thicker parts of the incrusta- 
tion the basal membrane may develop on its outer surface rather vaguely marked ridge-like thickenings, 
which by their union give rise to a strengthening network of tangential bands, thus suggesting on a 
most minute scale the arrangement of the trabeculae in the honey-combed species of Echinoclathria. 
(Ridley & Dendy, 1887, pi. 31.) 
Spicules. — Megascleres: (I) Stylus smooth, with the merest trace of a constriction just below 
rounded end, tapering to sharp point, 340 by 20 p, with smaller sizes present; echinating the radiating 
columns, issuing for the most part in tufts — especially from ends, though also from sides — of columns; 
projecting, also, singly or in small tufts, from the basal membrane; also included as an axial string 
(though in places absent) in radiating columns; included much less abundantly in basal membrane. 
(2) Slender subtylostylus, smooth and tapering to point, 280 u by 3 p a common size; abundant in 
parenchyma; also included, but not abundantly, in the several parts of the horny skeleton, especially 
in basal plate. Microscleres: (3) Small palmate isochela; 12 to 14 p long, very abundant throughout 
parenchyma. (4) Toxa 64 // long, smooth, and so slender as to be inconspicuous in balsam prepara- 
tions; fairly numerous in parenchyma, abundant in places. (5) Rhaphid oxea 300 p long, straight or 
somewhat curved; sparsely present here and there in parenchyma. These spicules are probably 
elongated toxas, as in some species of Clathria. I have not, however, seen transitional stages, owing 
possibly to the scant numbers of this spicule. 
A comparison of the Porto Rico form with Microciona prolifera Yerrill (Yerrill & Smith, 1874, 
p. 741) is interesting. The latter species is an incrusting form on shells and stones, common from 
