198 



ADDITIONS TO "BRITISH CONCHOLOGY. 



By J. T. MARSHALL. 



Part VII. (concluded from p. 174). 



Mr. James Simpson, who has had some experience of this curious 

 and interesting species, writes that although various species of 

 Echinidae are said to provide a host for the Stilifer, he has " never 

 found them on any other than the one species — Strongylocentrotus 

 drobachiensis Mlill., although Echinus esculentus [which is supposed 

 to be its favourite host] is quite as abundant on the same grounds."^ 

 He agrees generally with the observations of Gwyn Jeffreys, which were 

 founded on a pair of Stilifers dredged in the Shetlands,"-^ and he adds : 

 " Stilifer is invariably found among the spines on the upper surface of 

 the sea-urchin ; I have never seen them on the lower side near the 

 mouth. It creeps about the base of the spines by means of its com- 

 paratively large foot, and deposits its ova upon the urchin in a minute 

 oval gelatinous sac. Sometimes there are so many of these little 

 patches of ova that they give the urchin a somewhat diseased appear- 

 ance. One that I examined had 34 of these patches ; whether they 

 were all from the two Stilifers that were upon their host I am not 

 prepared to say. One of these sacs was more developed than the 

 rest, so much so that the little mollusc could have been identified by 

 its shell alone. As many as ten Stilifers have been found on a single 

 Echinus, but three seems to be the average." 



Mr. Simpson also writes that he is inclined to doubt Gwyn Jeffreys' 

 statement that Dr. MacGillivray's specimen was "a young West 

 Indian land shell belonging to the Cyclophoridse,"^ because, he says, 

 Stilifer is frequently found off Aberdeen, and that as MacGillivray 

 even mentions the finding by one of his pupils " of a specimen ad- 

 hering to an Actinia at Footdee as far back as 1842," he must have 

 been more or less acquainted with the shell, and that he gave a good 

 description of it in his " MoUusca of Aberdeen " under the name of 

 Stylina stylifera.^'' 



Eulima, Risso. — Gwyn Jeffreys has written that Eulima is '' not 

 parasitic,"^ and that although " species of Eulima have been found in 



the stomachs of HolothuriiE this is not a case of parasitism ; 



the Eulima feeds the Holothuria instead of feeding upon it." (p. 194). 

 This may be so in some cases, but subsequent research points to the 

 fact that certain Etilima are distinctly parasitic. Besides Professor 



1 Trans. Aberdeen W. M. Nat. Hist. Soc. , 1903, pp. 79-80. 



2 Brit. Conch., vol. iv. , p. 197. 



3 Brit. Conch.., vol. iv. , p. 196. 



4 Brit. Conch., vol. iv. p. 190. 



