IIYALEA. 379 



Our few British species are all members of the shelled 

 division of the order, and belong to two different families, 

 viz., the HyaleadtE characterised by their corneous sheath- 

 like, more or less triangular shells, and the Limacinad^e, 

 whose bodies are enveloped in regularly spiral shells, re- 

 minding us closely of those of many Gasteropoda. 



HYALEA, Ferussac. 



Shell thin, corneous or glassy, smooth or furrowed, more 

 or less globular, with a spine or angle at each side, and 

 one forming its posterior termination ; sides split, mouth 

 transverse, anterior, one of the lips overlapping. 



Animal with a globular body, having two wing-like 

 lateral expansions which are projected from the slits at the 

 sides of the shell, and a broad expanded two-winged 

 natatory disk, extending on each side of the anterior 

 extremity. Head not distinct. Branchiae lodged in a 

 special cavity. No operculum. 



The Hyalea are oceanic, and on account of their size and 

 colour are easily distinguishable in the water, especially 

 when the animal expands its swimmers and fins. It is by 

 no means improbable that more than one species may 

 occasionally visit the western shores of Britain, and those 

 naturalists who may meet with the fleets of IantMna and 

 Velellce which are occasionally wafted on shore in the west 

 of Ireland, the Hebrides, and the south-west of England, 

 would do well to search carefully among the debris, lest 

 Hyalea and allied Pteropods may accompany floating ani- 

 mals which are their constant companions in seas more to 

 the south. 



