On an apparently Neiv Form of 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 Holothurice. Viewed 

 thus, this little animal is fraught with interest, and may 

 serve to connect, by its gradation of form, the genus Holo- 

 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 appearance 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 maybe 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 fluid 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: — 



