REPOET ON THE TUNICATA, 
201 
The species of Aplidium in the Challenger collection may be distinguished by the 
following characters : — 
Aplidium. 
Outer layer of the test 
incrusted with sand. 
No incrusting sand. 
Colony incrusting, 
and attached hy a 
wide area. 
Colony not 
incrusting, attached 
hy a small area. 
Large horizontal 
membranes in 
the branchial sac. 
No well-marked 
horizontal 
membranes in 
branchial sac. 
A. crassum. 
A. inemstans. 
Colour grey. 
A. leucophceum. 
Colour brown. 
I 
A. fuscum. 
Stigmata small. 
Stigmata 
very large. 
Colour 
dark grey. 
1 
A. despectum. 
Colour dark A. fallcux. 
smoke-brown. 
A. fumigatum. 
These species are all new to science with the exception of Aplidium fallax, Johnston, 
a British species. 
Aplidium incrustans, n. sp. (PI. XXVII. figs. 3-8). 
The Colony is quite irregular in shape. It is a large expanded incrusting mass 
attached by the greater part of the lower surface. The upper free surface is convex. 
The edges are thick and rounded. The colour is a dark dull grey with light grey 
spots formed by the bodies of the Ascidiozooids. The surface is even and smooth. 
The length of the colony is 5 '5 cm., the breadth is 3 cm., and the average thickness 
is about 0'5 cm. 
The Ascidiozooids are large, measuring as much as 5 mm. in length. The greatest 
breadth is about 2 mm. They lie somewhat irregularly, but most of them are more 
or less at right angles to the upper surface. The part which is visible on the exterior of 
the colony is rather more than the anterior end, and forms a spot sometimes upwards of 
2 mm. in its greatest extent. There is no long post-abdomen, and no vascular appendages 
are present. 
The Test is soft, and tears readily. The external layer is rather firmer than the 
internal part, and is very smooth and glistening on the surface. Sand-grains are 
scattered sparsely all through the outer layer. In sections the test is seen to be crowded 
with cells of very considerable size and of various shapes. The commonest forms are 
triangular and stellate, with very long branched angles and processes. The nuclei are 
large and distinct. The matrix is clear and structureless. 
(ZOOL. CHALL. EXP. — PART XXXVIII. — 1886.) 
Pp 26 
