CHAP. V.] THE GULF-STREAM. 353 
the disk. This is a very widely distributed deep-water species. 
We met with it near Tristan d’Acunha, in the Southern Sea, 
and in the North Pacific. There is an allied species of the 
same genus somewhat more ornate, and of an orange instead of 
a blue color, in the China Sea. 
The same haul gave us a singular little addition to the family 
to which Pourtalesia and Aceste are referred. Aérope rostrata 
(Fig. 99) is a small species, little more than a centimetre in 
length. Like Powrtalesia, it is nearly cylindrical, and the odd 
inter-ambulacral area is greatly prolonged backward, and the 
excretory opening brought up upon the apical aspect. The 
apex with a peculiar madreporic tubercle, with large perfora- 
tions and four ovarial openings with long exsert-ovarial tubes, 
is a little in advance of the centre of the dorsal surface, and just 
Fig. 98.—Porcellanaster ceruleus, WyViLLE Tuumson. Dorsal surface. Natural size. (No. 45.) 
within a kind of disk surrounded by a semita. The anterior 
ambulacral canal runs down the centre of this disk, and gives 
off eight or ten disproportionately large tube feet with large 
terminal rosettes, as in Aceste. The mouth is round and oppo- 
