SNAIL SEA-CUCUMBER. 205 



ten in number. The vent is surrounded by a circle of 

 suckers. 



Dr. Johnston remarks on the skin, " The coat is divisible 

 into two parts, viz. an exterior scaly true skin of a sub- 

 calcareous texture, and an inner muscular layer formed of 

 ligamentous fibres arranged in close parallelism, and trans- 

 verse or circular in their direction, so that when in action 

 their effect must be a compression of the body, by which 

 it will be elongated and rendered slenderer. The pro- 

 trusile part of the mouth is entirely formed by a continu- 

 ation of this ligamentous coat, which likewise, in a more 

 delicate modification, forms the arborescent tentacula." 



When dissected, we find the generative tubes very long 

 and numerous, a very large oesophageal sac, and a respira- 

 tory tree moderately branched. The muscles of this ani- 

 mal are remarkably powerful. 



The Psolus adheres to substances with great firmness by 

 means of its ventral disk, much stronger than any of the 

 other Holothuriadce, as might be expected from the con- 

 centration of its locomotive organism. So powerfully does 

 it adhere, that I have known the head of the animal carried 

 away by the dredge when it brought up entire every other 

 fixed animal which it came in contact with. 



Pennant first recorded the species as British. He says 

 it was taken off Scarborough. Dr. Fleming states it is 

 occasionally found, from Devon to Zetland. Dr. Johnston 

 found it on the coast of Berwickshire. Mr. Goodsir has 

 twice procured it on the coast of Fife in deep water. I 

 have taken it in ten fathoms water in the Gair Loch, 

 opposite Helensburgh, on the Clyde. Mr. W. Thompson 

 has recorded it as obtained by him in 1835 at Bangor, 

 county of Down. 



