REPORT ON THE TETRACTINELLIDA. 
215 
2. Orthotrixne (PI. XXVIL fig. 4), a conical rliabdome with a strongylate termin- 
ation, and slender, cylindrical cladi, curving outwards and slightly forwards, with 
rounded or pointed ends. Ehahdome 0‘318 by 0'0158 mm., cladi 0’206 mm. long. 
II. Microscleres. 3. Sterraster (PI. XXVIL fig. 5), small, spherical, the ends of the 
actines granulated, diameter 0'0553 mm. 
4. Somal spherule (PL XXVIL figs. 6-9), a minute sphere with a smooth surface, 
0'00395 mm. in diameter. This occurs below the outer epithelium, and is distributed 
generally throughout the sponge. 
Colour. — Somewhat purple on the upper surface, yellowish-white underneath. 
Habitat. — Bahia, September 1873 ; shallow water. 
Remarks. — This sponge is represented by a single fine and perfect specimen, with one 
small, well-marked lobe, and a large, massive part indistinctly divided into two lobes. 
It measures altogether 130 mm. in length, 100 mm. in breadth, and 80 mm. in height. 
There are three oscules, one to each lobe; the largest is 11 mm. long by 8 mm. wide, 
surrounded by a smooth margin, 4 mm. wide. A smaller oscule, 10 by 6 mm., leads into 
a cloaca, 12 mm. deep and 11 mm. wide in broadest part; it is smooth and imperforate 
for 6 mm. from the mouth, for the rest of its extent its walls are a mere network, the 
meshes being occupied by the mouths of the excurrent canals. The excurrent canals 
extend through the whole length of the lobe in which they occur (PL XXVIL fig. 2). 
Ectosome. — The cortex (PL XXVIL fig. 13) is about 0796 to 0'92 mm., the ecto- 
chrote (PI. XXVIL fig. 14) from 0'05 to 0'24 mm. in thickness; the sterrastral layer 
varies but slightly on each side, 0‘65 mm. in thickness, and the fibrous layer is from 
0’05 to 0'08 mm. thick. On approaching the oscule the cortex is thickened to form its 
margin and inflected to be continued, somewhat modified, as the lining of the sides of 
the cloaca. There it becomes somewhat thinner, about 0‘636 mm. thick on the average ; 
the ectochrote with its thick crust of spherules is 016 mm. thick; the sterrasters are 
somewhat sparingly scattered through a fibrous tissue 0’238 mm. thick ; and the inner 
fibrous layer without sterrasters is also 0'238 mm. thick. 
The pores are chiefly circular, 0‘05 to 0'064 mm. wide. They are closely and 
uniformly distributed over the dermal membrane, not being collected into small circum- 
scribed groups (PI. XXVIL fig. 11); the very short poral canals unite together imme- 
diately below the surface, at first in groups of two forming wider canals ; and these 
are scarcely formed when they similarly coalesce in groups of three and four ; the larger 
canals resulting are separated by walls of vesicular tissue, covered with globules and the 
all-investing epithelium. The larger canals open freely at the bottom of the ectochrote 
into the outer end of the chones (PI. XXVIL figs. 12, 13); the ch ones are fairly, regularly, 
and closely distributed, varying from 0'253 to 0'5 mm. in diameter, more or less circular 
in transverse section, and on the whole more cylindrical than conical in general form. 
