MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 383 



The second pair of maxillipeds (Fig. 6) has a long, strap-shaped exopodite, like that of the 

 first pair. The eudopodite is incurved, aud segmented into at least four parts. The dactylopo- 

 dite or, terminal segment is the longest, and is thickly studded with serrate bristles and setse. 

 There is a small oval epipodite. 



The third pair of maxillipeds (Fig. 5) consist of a basal piece (coxopodite) and a long two- 

 branched appendage. The large branch consists of three distinct segments a long proximal one 

 (basipodite (?) aud ischiopodite), a shorter one (meropodite), and a long terminal segment (carpo- 

 podite, propodite, and dactylopodite). The exopodite springs from the base of the first segment, 

 and is about equal to it in length. The lower surface of the two terminal joints is covered by 

 numerous transverse rows of serrated bristles, and the end of this appendage is armed with several 

 spines. 



The first pair of pereiopods or walking legs bear the great chela? ("hands" or "shears"). 

 The chelae are very unequal. Large claw (relatively larger in $ ) smooth, slightly twisted; outer 

 and upper border sometimes marked by a linear crest; several spurs or tuberosities near the 

 articular surface of the dactyle; dactyle shaped like end of pruning knife, its concave inner 

 margin and tooth-like point shutting into a groove of the opposing "thumb." This groove of the 

 propodus is continuous with the well, in which the stopper-like tooth of the dactyle fits. It is 

 bounded by a rectangular process 'above and a less prominent one below. Tips of fingers barely 

 overlapping. Dactyle sometimes overreaches propodus. Thumb (or extremity of propodus from 

 joint of dactyle) one-third to one-half length "palmer portion "of propodus. Dactyle works some- 

 what obliquely. Tips of fingers simple. Propodus sometimes hooked. 



Small claw (Fig. 3, PI. xxiv) usually carried bent downward. Fingers nearly equal; three- 

 fourths as long as palmer portion of hand; bent slightly downward and outward; propodus sub- 

 cylindrical; half as broad as long; tip simple or slightly bifid. Small bunches of seta- on fingers. 



Second pair of pereiopods (Fig. 1, PI. xxm) : The characters of this appendage appear to 

 be remarkably constant aud of considerable specific value. They end in a small claw, the 

 fingers of which are provided with bunches of long hairs. Carpus superficially constricted into 

 live rings or segments. First or proximal segment nearly equal to 2+3+4+5. Second, third, 

 and fourth of nearly equal length; fifth equals 2+3. 



The third, fourth (Fig. 2, PI. xxm), and lit'tii pairs (Fig. 1, PI. XXIV) of walking legs are similar 

 to each other, the fifth pair beiug shortest. Each ends in a short, horny dactyle which is bifid at 

 apex, the primary claw bearing a smaller secondary tooth at base. Propodus little shorter than 

 ineros in the fifth pair, and carries numerous bunches of short setas on its under side. There are 

 also found in this region of the propodus four to six stout appressed spurs. 



The first pair of pleopods is specially differentiated in the sexes, and forms one of the most 

 convenient marks of distinction. The first abdominal limb of the male is shown in Fig. 4, PI. 

 xxiv, aud the corresponding appendage of the female in Fig. 5, and the typical appendage in Fig. 

 0. In the unmodified limb the protopodite carries as usual the two branches endopodite and 

 exopodite each fringed with long seta-. The eudopodite is a little longer than its fellow aud 

 bears a rudimentary secondary branch, which springs from near the middle of its inner edge. 

 In the male (Fig. 4) the appendage is considerably reduced. The exopodite is short and the 

 inner branch a small rudiment. Ill the female (Fig. 5) the modification has not proceeded so far. 

 The eudopodite is here the shorter and has no secondary branch. In the very young forms 

 (first larva;) these appendages appear to be nearly alike in both sexes (PI. xxu, Fig. 5). 



The uropods or sixth pair of pleopods hardly require special notice (PI. IV). The eudopodite, 

 much the smaller division, is an oval plate, aud on its upper side there is a roughened median 

 ridge. The free edges of the plates are fringed with long and closely set plumose set;e. 



V. VARIATIONS FROM THE SPECIFIC TYPE. 



We are now ready to consider the remarkable variations which this species undergoes. The 

 form just described was taken as typical, and the largest adults invariably belong to it. 



(1) Variety L<t<jic<u-piin: This is the widest departure from the first form or type and is very 

 commonly met with in the brown sponges already noticed. Probably more than 'JO per cent of the 



