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THE VOYAGE OF H.M.S. CHALLENGER. 
arranged in simple or double alternating rows. The two dorsal ambulacra have conical, 
non-retractile processes in a zigzag row. The interambulacra naked. Deposits — small 
reticulate cups with very spinous rims ; crowded symmetrically formed buttons, with 
as a rule four holes and about ten knobs ; and larger scales resembling simple per- 
forated plates with uneven surfaces. Colour in alcohol, brownish. Length about 25 mm. 
Habitat. — Bahia, September 1873 ; depth, 7 to 20 fathoms; a single specimen. 
The body of this small species is provided with sharp angles along the four 
ambulacra, and with a more obtuse angle along the odd ventral one. As noted in the 
diagnosis, the pedicels and processes are confined to the ambulacra, but, to judge from the 
only specimen I have seen, a tendency to spread over the odd dorsal interambulacrum 
may be observed, a few very minute processes being situated near its middle line. 
There is no doubt that this species is nearly related to Ludwig’s Colochirus austfalis, 
though it difiers from it in several important characters. Thus, the scales in the 
perisome are especially distinct, those of Colochirus australis being much larger, thicker, 
and composed of several superposed layers, thus constituting true net-shaped scales, 
while the “ scales ” of Colochirus pygmoeus (PL IV. fig. 9a), composed of a single layer, 
resemble common, simple perforated plates, and do not exceed 0‘5 mm. in length. 
These scales or plates are not crowded, but very scattered ; they are mostly of an 
elongated form, several times longer than broad, and have the surfaces uneven from the 
presence of low knobs or elevations. The buttons (PI. IV. fig. 9&) have a diameter of 
0'08 mm., but often much smaller ones may be found ; they do not seem to vary greatly 
in general appearance. The cups (PI. IV. fig. 9c, d), which lie most externally in the 
perisome, are very minute, 0‘028 mm. in diameter, and deeply hollowed; their free 
rim is provided with numerous processes or spines. The entire cups are built up of 
a strong x -shaped body with the arms curved, sometimes slightly branched. The 
pedicels and processes are supported by transverse, perforated rods, mostly with a third 
arm at the middle (PI. IV. fig. 9e). 
From want of materials, I could not examine the internal organisation. 
Genus Actinocucumis, Ludwig, 1875. 
Actinocucumis typica, Ludwig, 1875 (PI. XII. figs. 4, 5). 
Habitat. — Station 186, September 8, 1874; lat. 10° 30' S., long. 142° 18' E. ; 
depth, 8 fathoms ; coral mud ; a single specimen. 
There is nothing to add to the description of Ludwig, excepting that I find some 
minute papillae even on the ventral surface in the anterior and especially in the posterior 
parts. The pedicels seem to be rather stiff. According to Ludwig, the species has been 
previously obtained from Amoy (China) and Bowen (Australia). 
