eee.’ 
A BOX OF BRANCHIA’ 369 
CHAPTER XXIII 
TRIBE III.—VALVIFERA 
HERE the uropods undergo a remarkable metamorphosis, 
and assume a function distinct from any that they have 
elsewhere, for like a pair of folding doors they form a great 
part of the ventral surface of the pleon, these valves closing 
over the five pairs of branchial pleopods or opening to 
admit the water to them. 
In the ‘ History of the British Sessile-eyed Crustacea,’ 
vol. il. pp. 358, 368, 375, 378, the uropods are successively 
spoken of as ‘ the first or anterior pair of pleopoda,’ as per- 
taining to ‘the first segment of the tail,’ as being absent in 
the Idoteide, where there is said to be a ‘conversion of 
the fifth pair of pleopoda into a continuous operculum for 
the protection of the branchial organs,’ and lastly, in the 
genus Idotea, as ‘a strong outer pair (which are the ter- 
minal uropoda), forming an operculum’ over the ‘five 
pairs of very delicate branchial appendages.’ Of these 
four statements the first two are consisteat but erroneous, 
the last two are inconsistent with the first and with one 
another; only the final one is correct. All the four, as it 
happens, appeared in the same number of the work, namely, 
Part 19, published October 1, 1867, so that the confusion 
is difficult to account for, even as an accident of dual 
authorship. 
The tribe includes two well-separated families, the 
Arcturide and Idoteide. 
Family 1.—Arcturide. 
The form of the animal is elongate and sometimes 
cylindrical; the segments of the pleon are more or less 
