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 Megamoera 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 Sulcator there are no less than 

 twelve varieties. Some are plain, stiff, bristle-like 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- 



