328 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



(2) The Hyperina, with large head and eyes, which 

 swim rapidly, and are frequently found as commensals in 

 jellyfish. 



(3) The Gtammarina, with comparatively small head 

 and eyes, including the Corophiidse which move chiefly 

 by walking, the Orchestiidse of which many species live 

 on the land and move by springing, and the Gammaridse 

 which move more by swimming than jumping. 



The Amphipod chiefly described below is Gammarus 

 pidex, first so named by Fabricius (6) in 1775, but previ- 

 ously referred to by Greofrroy (7) in 1762, as " La crevette 

 des ruisseaux," and probably the " Cancer ptdex occurring 

 both in fresh and salt water," mentioned by Linnaeus (12) 

 in 1767. It was described by Zenker (28) in 1832, but his 

 conclusions are not in agreement with modern investiga- 

 tions. Sars (20) figured and described it in 1895. He 

 regards it as synonymous with Gammarus fluviatilis, 

 Milne-Edwards, G. lacustris Sars, G. neglectus Sars, and 

 G. locusta, var. B., Hoik. For the convenience of those 

 working at the seaside, a comparison is made, where 

 necessary, with the corresponding parts of the commonest 

 marine species — G. locusta. 



Gammarus index, as was observed by Turton (23) as 

 early as 1802, is very common in running water in 

 temperate climates. Zenker (28) remarks that it is 

 " universally distributed in the rivers and streams of 

 Europe." It is also found in lakes and ponds. 



The creatures bury themselves beneath loose leaves, 

 bits of wood, &c, and, if disturbed, dart rapidly back into 

 shelter, evincing a strong disinclination to remain in the 

 light. When at rest, they lie curled up on one side. 

 The last three thoracic legs, or perseopods, are bent back 

 and up, so that their tips project above the back. These 

 attach the creature to the under side of a dead leaf, or 



