INVERTEBRATE BOTTOM FAUNA 495 



notwithstanding the apparently suitable bottom of stones and 

 shells, is very remarkable, a few specimens of Lepidopleztriis 

 {Chiton) cinereiLS at one station (57 metres, temperature 7.9'" C.) 

 being all that we met with. 



The bottom of the North Sea abounds, as already stated, 

 in empty shells, particularly of mussels. The commonest forms 

 are Cardium echinatinn, Cyprina islandica, Venus gallina, 

 Dosinia lincta, Mactra, Psanwiobia ferroensis, So/en, etc., all 

 of which were likewise taken alive. Lucina borealis, on the 

 other hand, though shells were met with here and there at a 

 depth of 38 to 98 metres, sometimes even in fairly large 

 quantities, was not captured alive out in the North Sea by 

 us, and the "Pomerania" Expedition obtained only empty 

 shells on the Dogger Bank ; it is not included by Heincke 

 amongst the molluscs of Heligoland, but we do find it along 

 the coasts of Britain and in the Skagerrack. Empty shells of 

 Alya truncata forma typica were also found in two localities, 

 one at a depth of 14 metres off the north-west coast of Jutland, 

 and the other midway between Jutland and Scotland at a depth 

 of 68 metres. 



The higher crustacean fauna is comparatively poor in species, 

 most of them being restricted in distribution and few in numbers. 

 The hermit crabs Pagm^us bernkardns and P. p2ibescens are 

 exceptions, as they are pretty generally distributed over the 

 whole area, though only the first named is met with in shallow 

 water, at or below 40 metres ; at greater depths both species 

 occur, as in some other areas of the North Sea. Of crabs Hyas 

 coarctattts is common in both deep and shallow water, whereas 

 Portunus depiLrator (or holsatics^) and P. pusillus are more 

 limited in their distribution, and occur mainly in the lesser 

 depths. Other forms are more local, though frequently met 

 with in considerable numbers, like the little Porcellana longi- 

 cornis ; as a contribution to its biology I may mention that we 

 found large numbers at two stations (depth 32 metres and 42 

 metres, temperature 10.9° C. and 8.7° C), where in one case 

 it had crept into the holes made by the borer-mussel (Pholas 

 crispata) in sunken pieces of timber and in the other it occu- 

 pied cavities in the large clotted lumps of sand constituting the 

 colonies of the tube-worm Sabella^Ha alveolata. At greater 

 depths it was absent, Porcellana being to a great extent a 

 littoral form.^ 



^ We also found two other crabs in shallow water west of Jutland (32 metres) : the ordinary 

 edible crab {Cancer pagiirus) and Hyas araneus. Single specimens of two species of Ebalea 



