350 
THE VOYAGE OE H.M.S. CHALLENGER. 
upwards to open freely into the cloaca ; incurrent canals radiating from the general 
surface towards the cloaca. 
Spicules. — I. Megascleres. 1. Desma, small; epirabd somewhat straight or tri- 
radiate, frequently straight and bifurcate at each end, bearing conical spines ; cladus of a 
triradiate form, O'l by 0'019 mm,; crepidial axis short, from O’Ol to 0’0275 mm. in 
length; zygosis general, but chiefly terminal. 2. Tylostrongyle, slender, cylindrical, 
0’48 by 0‘005 mm. 
Colour. — Brown . 
Habitat . — West Indian Islands; lat. 25° 23' N., long. 83° 31' W. ; depth, 101 
fathoms. Lat. 22° 9' 15" N., long. 82° 20' 80" W.; depth, 127 fathoms, 
Remarhs. — The water-canals are lined by a thick layer of collenchyma, in which 
desmas do not occur ; microscleres if present would certainly be found here, and as they 
are not their absence has been positively ascertained. The coUenchymatous walls re- 
semble those of Theonella (PI. XXX. figs. 9, 10) and other Lithistids. 
The tylostrongyles occur in bundles throughout the sponge ; near the surface they 
are directed at right angles to the epithelium, against which the tylote ends of the most 
external of them abut. They are never arranged tangentially to form an ectosomal layer. 
The surface of attachment is covered by a smooth shining layer produced by modified 
desmas. 
Genus 4. Setidium, 0. Schmidt. 
Diagnosis not given. 
Setidium obtectum, 0. Schmidt. 
Setidium ohtedum, 0. Schmidt, Spong. Meerh. Mexico, p. 30, pi. i. fig. 9, pi. ii. fig. 14, 1879. 
Sponge. — Cyathiform, with thick walls and rounded edges, attached by an expanded 
base. Inner and outer surfaces, but not the edge of the cup, bearing numerous, more or 
less regularly arranged, somewhat conical processes, each bearing a bundle of about six- 
teen to eighteen long oxeas. Each process covers the end of a canal, which is lined by a 
layer of similar oxeas. 
Spicules. — I. Megascleres. 1. Desmas, densely tuberculated, forming a more than 
usually hard and stony skeleton. 2. Oxea, long. 
Habitat. — Near Havanna ; depth, 128 to 240 fathoms. 
Remarh. — I have not seen this sponge, so that I am unable to give an account of 
the skeleton. 
