342 
THE VOYAGE OF H.M.S. CHALLENGER. 
are characteristically monocrepid, and hence I refer the sponge to the Corallistidae, but 
now and then one meets with a true skeletal desma in zygosis wuth its fellows, and pre- 
senting the additional three short actinal axes described by Schmidt. I was at first, from 
the rarity of this phenomenon, inclined to imagine that Schmidt might have been mis- 
taken, but after considerable pains I obtained the clearest evidence to the contrary, and 
I am now convinced that a complete series of transitional forms connect the monocrepid 
and tetracrepid desmas. 
Genus 4. Dsedalo'pelta, n. gen. 
Corallistidse in which the desma and discotrisene are similar to those of Macandrewia, 
but the microscleres are spirasters. 
Dsedalo'pelta nodosa (0. Schmidt). 
Discodermia clavatella, var. nodosa, 0. Schmidt, Spong. Meerb. Mexico, p. 25, pi. iii. fig. 1, n. o., 
1879. 
Spo'nge . — A small cushion-shaped mass, attached by an irregular base ; surface some- 
what rough, except over the base and sides, which are smooth and shining. Oscules 
numerous, small, simple openings collected within two shallow depressions on the upper 
surface, leading into small canals which radiate into the sponge in all directions, the most 
superficial visible beneath the skin, arranged in a branching stellate system. 
Spicules . — I. Megascleres. 1 . Desma, epirabd quadriradiate, triradiate, or more or 
less straight, smooth ; cladi smooth or tuberculate ; zygosis chiefly terminal. Maximum 
total length of a rectilinear form, 0’4 mm. Crepidial axis usually centrotylote, 0'047 mm. 
long, varying but slightly on each side of this to 0'043 and O’OSl mm., in one excep- 
tional instance 0'095 mm. in length. 2. Phyllotrisene, cladome consisting of irregular 
narrow cladi, margins produced into bifid spines, or bifurcating tubercles which end in 
bifid spines ; upper surface also tuberculated, the tubercles bearing from one to four bifid 
spines. Maximum diameter of the cladome, 0‘35 mm. Ehabdome conical, strongylate, 
0'05 to O'l mm. in length. The axial fibre of the cladi seldom more than 0‘009 mm. in 
length. 3. Oxea, slender, cylindrical, 0’2 by 0'003 mm. 
II. Microscleres. 4. S'pirastei', variable in form, sometimes passing into an amphi- 
aster, sometimes into a metaster, 0'0237 mm. in length; a single spine often O'Ol mm. 
long. 
Colour. — Dark brown. Size, 33 mm. long by 26 mm. wide and 13 mm. high. The 
smooth basal surface extends up the sides for a distance of 3 mm. 
Habitat . — Gulf of Mexico. 
Remarks . — The smooth basal surface is produced by a layer of closely articulated 
