Sea-slugs 273 



tendinf^ backwards over part of the shell. It is 



tolerably plentiful along our sandy bays, between 



15 and 50 fathoms, where it grubs, pig-like 



in the sand for food with its flat snout. 



When irritated it pours out a yellow fluid, 



apparently to drive off enemies. A smaller 



species, the White Bubble {G. alba), has been 



taken in deep Avater on fine sand off Unst, B^bble^'-she'ii 



Shetland (84 to 95 fathoms) ; Butt of Lewis 



(189 to 530 fathoms); West of Ireland (430 to 1366 



fathoms). 



The Glassy Bubble-shell (Amphisphyra hyalina) 

 is oval, equal at both ends, of glass-like clearness, 

 and about a fifth of an inch long. The whitish 

 animal has a bilobed head, with small eyes, which 

 are withdrawn into the shell when the animal is at 

 rest, but show through. It is a native of the lamin- 

 arian zone. There are three other species, found in 

 Skye and Shetland. 



The typical Bubble-shells {Bulla) are solid, with 

 the crown perforated and exposing part of the spire. 

 B. utriculiis has an oval glossy shell, fairly solid 

 yet semi-transparent, with impressed spiral lines. It 

 is only half an inch in length, and is found in muddy 

 sand in from 20 to 86 fathoms on various 

 parts of our coast. B. seinilevis was taken 

 off the south of Ireland in 1000 fathoms 

 by the Flying Fox expedition, 1889. 



The Southern Bubble - shell {Haminea 



hydatis) is distinguished from Bulla, with 



which formerly it was associated, by being 



thin, the crown not perforated, and the outer lip so 



expanding as it grows that the spire is completely 



