346 
THE VOYAGE OF H.M.S. CHALLENGER. 
in diameter at the base, which is broken ; the oscular tubes do not exceed 1 mm. in 
diameter. 
Hahitat. — Barbados ; depth, 103 fathoms. 
Remarks. — A small specimen nearly 3 mm. in diameter, presents in transverse 
section the cut ends of six longitudinal canals, bounded towards the interior and laterally 
by the desmose skeleton, and on the exterior by the layer of discs ; no other distinct 
canals were seen. The longitudinal canals are seen below the discs when the ectosomal 
layer is viewed en face, they are crossed by velar diaphragms, and are evidently sub- 
dermal or ectosomal in the strictest sense. Although portions of the ectosome measuring 
altogether about 4 mm. square were prepared with a view to examining the pores, only 
one pore was found. 
The appearance of the skeleton is very tetracladine, but the desmas are all strictly 
monocrepid. 
Family II. Scleritodermida:. 
Genus 1. Scleritoderma, 0. Schmidt. 
Scleritoderma packardi, 0. Schmidt. 
Scleritoderma paccardi, 0. Scliinidt, Spong. Meerb. Mexico, p. 28, pi. ii. fig. 3, 1879. 
Sponge. — A short wide cylinder with rounded edges, constricted above the flattened 
attached base, and depressed at the summit into a bowl-shaped cavity ; in other words, a 
depressed bowl-shaped sponge with thick walls and an expanded base. Oscules regularly 
distributed over the interior of the cup, opening at the summits of small rounded tubercle- 
like elevations, surrounded by a thick sphincter of concentrically arranged myocytes, 
OT to 0'15 mm. in diameter. Pores regularly distributed over the outer surface, simple, 
situated at the bottom of shallow circular depressions, about 0T3 mm. in diameter, closed 
by a sphincter of concentric myocytes. Surface smooth, in the neighbourhood of the 
pores very sparingly hispidated by an occasional oxea, which extends 0*5 mm. beyond 
the skin. 
Spicules. — I. Megascleres. 1. Desma, cladi highly tuberculate, zygosis close, dense, 
occurring along the sides as well a,s at the termioations of the cladi. 2. Oxea, cyhndrical, 
slender, only slightly curved, 1‘2 by 0‘015 mm. 
II. Microscleres. 3. Microstrongyle, irregularly fusiform, depressed, 0'17 by 0'013 
mm. 4. Sigmaspire, 0‘014 mm. long. 
The microstrongyles form a dense layer beneath the outer epithelium, lying tangen- 
tially, with their depressed surfaces parallel to the exterior ; they also occur throughout 
