EEPORT ON THE ISOPODA. 45 



males. lu the Challenger collection the two largest specimens measure 32 mm. iu length 

 by 24 mm. in breadth, and are females with developed brood lamellae. The males are 

 proportionately broader than the females ; the length of the largest specimen is 28 mm., 

 its breadth 24 mm. ; in one specimen only the breadth was proportionately less than in 

 all the rest, 28 mm. in length by 22 mm. in breadth ; the sterna of the free abdominal 

 segments differ but slightly in the two sexes — in the females all have a short, broad, 

 median spine, in the males the two posterior segments are provided with such a spine, which 

 is if anything rather smaller than in the female. 



The colour of Serolis latifrons (in alcohol) is a dark bluish brown, becoming lighter 

 brown upon the epimera ; a very characteristic mark of the species is a white spot upon 

 the anterior part of the cephalic shield, just behind the rostrum ; the fifth pair of epimera 

 also are generally lighter in colour than the rest of the body. 



The six posterior thoracic epimera are separated from the terga by a distinct suture 

 and the first abdominal segment, which in no other species of Serolis known to me has 

 any trace of epimera, has distinct though very minute epimera separated from the tergum 

 by a suture which is continuous ■ndth that dividing the epimeron and tergum of the 

 segment in front. 



Appendages. — The second paii' of autennse are longer than the first pair ; the latter 

 have as usual four joints; the fourth joint is extremely short, its length being only one- 

 third of its breadth ; the filament has sixteen joints ; in the second pair of antennas the 

 terminal joint (PI. II. fig. 4) is prolonged on the ventral side into a process which extends 

 as far as the third joint of the filament ; the filament has twelve joints. 



The mandibles are characterised by the great length of the narrow distal half, which 

 is about half the length of the entire appendage; the masticatory portion of the two 

 mandibles are shown on PI. II. figs. 2, 3; they present the usual unsymmetrical disposition 

 of the laminae and spines upon the lower surface. 



The first pair of maxillce resemble the same appendages in other species, but the 

 second joint of the palp has seven or eight spines upon its extremity instead of two. 



The second maxillce present no difi'erences from other species. 



MaxiUipedes. — The lamina and stipes are separated by a complete suture ; the 

 outer margin of the stipes and cardo is clothed with fine delicate hairs ; the lamina is 

 furnished on its under surface with a number of long hairs which extend over the 

 proximal joint of the palp. 



The first ambulatory limb presents no special difi"firences from that of other species. 



Of the second pair in the male, the penultimate joint is rather narrow, only slightly 

 wider where it articulates with the preceding joint; the distal joint terminates in a 

 spine-like extremity which is separated by a suture; just behind the articulation of this 

 spine is a ridge bearing a row of fine hairs. The remaining joints of this limb are 

 almost smooth, and have only a few short hairs. 



