MARSHALL: HABITAT OF MONTACUTA FERRUGINOSA. 40 1 



nost for the Montacutce it is not very much unhke Spatangus 

 Mrpureus. 



The Echinocardium in Torbay buries itself six or eight 

 inches deep in fine muddy sand, leaving no clue after the 

 receding tide as to its whereabouts, nor does it rise to the surface 

 on the approach of the returning tide, but it keeps up a com- 

 munication with the outer world by a burrow having an opening 

 like a 'three-cornered star. The sandy mud in which it dwells 

 is very tenacious, and its spines are so short and close set as to 

 be unable to afford a nestling place for Montacnta ferniginosa. 



However, lately digging up some Echiiwcardhun in Torbay, 

 I accidentally found a pair M. ferniginosa in close proximity to 

 one of them, which set me searching further, when I was 

 gratified by finding M. ferniginosa a regular attendant upon it. 

 On carefully dissecting a spadeful of sand containing one of 

 these echinoderms, I found a burrow leading from its ventral 

 end running irregularly in a sloping direction for three or four 

 inches, and in this burrow or track dwelt the Af. ferniginosa. 

 They were not in actual touch with its host, but followed at an 

 interval of an inch or so. This track is made by a current 

 from the echinoderm, and is almost exactly the width of J\f. 

 ferniginosa, enabling it to approach or recede, but not to turn 

 round. Owing to the clinging, tenacious character of the 

 muddy sand, with a little care the whole burrow and its denizens 

 can be accurately exposed. 



For the purposes of this paper I have dug up at least loo 

 Echinocardium cordatian^ and quite 60 per cent, had its attend- 

 ant M. ferniginosa ; where absent, I concluded it was owing 

 to my not hitting the line of cleavage of the burrow, and that 

 every echinoderm probably has its attendant or attendants— 

 usually one adult, then a string of from three to five immature 

 examples, always ranging from the largest, about an inch off the 

 echinoderm, and tailing down to the smallest, which probably 

 dwindle to the mere fry, but obviously are difficult to detect in 

 the rough-and-ready way of turning over a spadeful of sand. It 



