IDOTEA TRICUSPIDATA. 381 
on each side of the body, whilst other specimens are 
marked, often irregularly, with large pale yellow or orange- 
coloured patches on the body and tail. According to our 
own experience, the colour of the animal is dependent 
upon that of the weed on which it lives. Those that 
live on the black fucus are generally very dark purple, 
while those that we find on the green Alge are brightly 
verdant; and it has always been our opinion that this 
change was due to the food, as we have little doubt but 
that they are vegetarians in diet, and that the depreda- 
tions on fish is that of their marine companions. 
SW, eer 
The ‘accompanying woodcut exhibits different varieties, 
showing the comparative paucity of the articulations in 
the flagellum of the lower antenne in young individuals, 
the length of the three individuals whose antenne are 
delineated being indicated by the three adjoining lines, 
whilst the other figures exhibit variations in the form of 
the terminal segment of the body, with the length and 
size of the respective specimens in the British Museum, 
the first, third, and fourth of which are from Cornwall 
(B. M. Coll. No. 50, 94, and 45, 189), and the large 
second one from Cardiff (No. 56, 73). Some very fine 
specimens taken off Cornwall have the caudal extremity 

terminating in three well-defined cusps, as also one sent 
to us by Mr. Gosse from Torquay. 
Specimens having the extremity of the tail truncate, 
