ISOPODS OF NORTH AMERICA. 53 



animal tapers irregularly, the center person-segment being narrower 

 than its neighbor, as is also the case in S. titdes, and the pleon tapers 

 more suddenly than the perseon as far as the base of the sixth seg- 

 ment, the sides of which diverge to the point of insertion of the 

 uropods and then suddenly converge to a central and somewhat 

 upturned, much produced, apical process. Of the perseon- segments 

 the last two are the shortest. The first five segments of the pleon are 

 nearly equal in length to one another; only the second has lateral 

 spine-like processes, but here they are large, produced, and very 

 conspicuous. 



"The upper antennae have the basal joint large, in the male stout, 

 shorter than the cephalic plate, in the female dilated at the base, 

 longer than the cephalic plate, in both ciliated on the margins; the 

 second joint is short, dilated distally; the third is about half the 

 length and breadth of the second; the flagellum consists of one long, 

 succeeded by four short, articulations; the secondary appendage is 

 rudimentary and represented by only one minute articulation. The 

 lower antennas have the basal joint as broad as it is long, the three 

 following joints short, the fifth long and slender, carrying on the 

 outer side two pear-shaped vesicles; the flagellum is three jointed, 

 the second and third joints furnished with long cilia. 



"The first gnathopods have the soldered coxal portion folded beneath; 

 the basos broad and short, the ischium wanting; the meros narrow at 

 the base, then dilated, and ending in a point; the carpus in the male is 

 a little longer than the meros, which it overlaps; it is 1 pointed distally, 

 its sinuous margins are nearly parallel; upon it the huge hand is set 

 hammer-wise. In shape the hand is roughly triangular; a line from 

 the base of the finger to the stout horny thumb may be considered the 

 base of the triangle; along this (palm) margin is set a row of flat little 

 teeth, all but one or two of them lying closely side by side; one of the 

 sides of the triangle runs from the thumb-nail backward, receiving 

 the wrist in a sinuosity about the middle; the remaining side is formed 

 by the curved line running from the hinder extremity of the last- 

 described side to the base of the finger; the finger, which is short and 

 stumpy, with a nail like the thumb-nail, doubles closely down upon the 

 palm. In the female the wrist is considerably longer than in the male, 

 and is of the same breadth at both ends, but has a narrow neck near 

 its base; the hand in this sex is attached to the wrist by the apex of 

 the triangle; the thumb is a long process projecting from the base of 

 the triangle and causing the finger to project in like manner, and the 

 hand is thus of very different form from that of the male, being ovate; 

 the inner margins of both thumb and finger are irregular; the thumb 

 is truncate and has the horny nail set close to the outer margin; the 

 nail of the finger closes down into the cavity within the thumb-nail 

 and on the truncated end of the thumb. 



