XXII INTRODUCTION. 
Although we believe that the microscopic examination 
of the skeleton in these animals would frequently facili- 
tate the determination of doubtful species, yet it is a con- 
dition that is not to be trusted to alone, inasmuch as it 
is not unfrequently found that similar appearances are 
repeated in very distinct genera. Examples of this may 
be found on comparing the structure of Megamera Otho- 
nis with that of Chelura terebans. 
The form and structure of the hairs that are found on 
these animals, when microscopically examined, are of a 
very distinct and different character. They not only 
vary in separate species, but differ in several parts of 
the same animal. In Swlcator there are no less than 
twelve varieties. Some are plain, stiff, bristle-hke spines 
of various lengths, which are generally attached to 
the margins of the limbs. A second variety, longer in 
general form, fringed on one side with a series of fine, 
straight, teeth-like processes, possessing a rake-like cha- 
racter, is attached to the third siagnopod ; as is also 
A third, that differs from the preceding in having the 
teeth bent in a curve directed to the base. 
A fourth is found on the carpus of the second pair of 
gnathopoda. In this position are also two varieties, which 
originate from closely approximating bases. One is long, 
slender, and clean to the tip, where a few exquisitely 
fine cilia appear, which give to the extremity a bulbous 
appearance, that can be resolved only with a high (700) 
magnifying power. The other, or 
The fifth, is short, broad, flat, terminating in a point that 
is sharply bent upon itself; the lateral margins are like- 
wise furnished with a series of sharp denticles, ranged on 
each side, pointing to the base for about two-thirds of its 
length. 
A sixth is found on the propodos of the same appen- 
a 
