FROM THE EDDYSTONE GROUNDS TO START POINT, 451 



smaller quantity than on the neighbouring coarse gravel of Ground XI. 

 Ground X., as Chart II. shows, is surrounded by grounds on which 

 H. halecinmn is abundant. As has been already explained (p. 416), 

 this ground is occupied almost exclusively by Ophiothrisn fragili% but 

 occasional specimens of H. halecinum were taken upon it in some 

 hauls. A single specimen of the hydroid occurred in haul 10 on the 

 clean shell gravel of Ground IX., close to the Eddystone rocks, a 

 ground upon which hydroids were practically absent. It was occasion- 

 ally taken on the Bolt Head Shell Gravel, but never on the Prawle 

 Stony Ground. 



On the grounds where the species was most abundant the specimens 

 of Halcciinii halecinum were in by far the greater number of instances 

 fixed to the leathery tubes of Chaetoptcrus, the distribution of which, as 

 will be seen by comparing Chart II. with Chart X., is practically 

 identical with that of the hydroid we are considering. But in addition 

 to the Chactoptents tubes the hydroid was also found, though much 

 less frequently, attached to shells or (in haul 100 only) to stones. The 

 shells of Tapes virginea and Pecten opercularis were the most common 

 ones used by the hydroid, but exceptionally fine colonies were some- 

 times found attached to the flat upper valve of living Pecten maximus. 

 This latter mollusc was generally present on the Halecium grounds, but 

 only a comparatively small proportion of the specimens had colonies 

 of the hydroid growing upon them. 



Undoubtedly the presence of Chaetopterus in numbers, by offering a 

 suitable fixing place for the hydroid, is an important factor in deter- 

 mining the abundance of Halecium halecinum upon the grounds where 

 it is found in quantity. At the same time it is not the only cause, 

 since Chaetopterus is obtained in numbers on a ground some four miles 

 south-west of Iiame Head, where Halecium halecinum is by no means 

 plentiful. 



Distribution. Geographical. North Cajie, Norway, Baltic, Kattegat, Nortli Sea, 

 British and French Coasts, Mediterranean, Massachnsetts Bay {fide Hartlaub, No. 38). 



Depth. 12-50 fathoms (Sars,/de Hartlanb). 



Habitat. On shells, stones, etc., in hoth shallow and deep water, Init more usually the 

 latter (Hincks). Schulze (No. 105) states that in the rommcrania dredgings the species 

 was found on bivalve shells, worm tubes, etc. It was taken six times on stony gi'ouud or 

 sand with stones, four times on sand and shell, and twice on mud. 



Halecium Bcanii (Table VI., p. 529) was met with on all the grounds 

 upon which H. halecinum was found, although it was by no means 

 so abundant as the latter species on the grounds to the westward of the 

 Eddystone. It was found, so far as I remember, for I have no definite 

 records on the point, more frequently upon shells than on Chaetopterus 

 tubes, differing in this respect from H. halecinum. 



Distribution. Geographical. British Seas; Azores (450 fathoms, CAaZZ<;?iirer, Allman, 

 No. 3), south-east coast of Australia (150 fathoms, ditto); Mediterranean (Carus, No. 14). 



