On an apparently Neio Form o/Holothuria. 333 
and turns round to what appears to be its ventral surface. 
In the anomalous genus Psolus, as is well known, the loco- 
motive organs are restricted to a small flattened ventral disk, 
on which the three developed rows of feet are disposed. 
The arrangement of the feet in the animal under consider- 
ation is another instance of a like specialization of function, 
and indicates the tripod nature of the Holotlmrice. Viewed 
thus, this little animal is fraught with interest, and may 
serve to connect, by its gradation of form, the genus Eolo- 
thuria, with its five well-developed rows of locomotive feet, 
and the genus Psolus. 
The tentacles (PI. XVI. fig. 2) are ten in number ; eight of 
them are long, pedunculated, and alternately branched; and 
the other two are short and divided at their tips. They are 
all of a pale-yellow colour, very pellucid, and are about a 
fifth of the length of the body when it is fully extended. 
The two short tentacles correspond to the two tuberculated 
rows of feet of the dorsal aspect. 
The body of the animal is covered with calcareous plates 
of an irregular form, perforated by nearly circular apertures 
(fig. 4). The plates found in the feet of the three ventral 
rows (fig. 7) are spindle-shaped ; but they change their form 
in the feet immediately surrounding the head (fig. 8), and 
become in ap])earance very similar to the plates found on 
the body-skin. The plates of the dorsal tubercles and feet 
(fig. 3) resemble in their irregularity the plates of the body 
of the animal; and the same may be said of the plates occur- 
ring in the tentacles (fig. 6), in which they may be found 
extending to their ultimate divisions. 
The very delicate structure of the feet enabled me to 
examine them microscopically in the living animal ; and 
when so examined, a continuous circulation of a minutely 
granular fiuid may be seen, the current consisting of two 
streams — one passing along one side of the foot to the suck- 
ing-disk, and the other flowing back from this structure to 
the body of the animal. 
This little creature evidently belongs to Linnseus's genus 
Holothuria, which Van der Hoeven has lately revived with 
the following signification: — 
