44 
ORCHESTinm 
formed of two equal lobes. The second scale-like joint 
of the last three pairs of legs is oval. The caudal ap- 
pendages are short and strong. 
The animal generally is longer and more compressed 
than A. Nilssonii. The dorsal ridge is slightly elevated 
into a carina, which is most conspicuous towards the pos- 
terior limit of each segment. This gives to the animal, 
when viewed laterally, an imbricated appearance, from 
which circumstance we have taken the name, and by 
which the species can easily be determined from any other 
known British form. 
A. imbricatus appears to be rather local. The first 
specimens that we received were from Penzance, where 
they were taken by Mr. George Barlee, between tide- 
marks. In company with Professor Kinahan we have 
found them on the Breakwater at Plymouth, where they 
live in small pools left in the holes worn by the wash of 
the sea in the surface of that stupendous work. We found 
many individuals, and they appeared to be the only species 
of Amphipod that existed there. The colour was a bluish- 
grey, but a few were almost black. 
The following vignette is a sketch of the Western end 
of the Breakwater by Mr. Philip Mitchell, of Plymouth. 
