REPORT ON THE ISOPODA. 41 



Tlie Challenger obtained a great number of specimens of Scroll's sclnjthvi, raugino- 

 from the Gulf of Peiias on the north, to the Falkland Islands on the south. 



The collection of Crustacea in the British Museum contains one specimen which is 

 labelled "New Zealand," but I believe that it is not quite certain whether this label be 

 correct. With this possible excej^tion, Serolis schythei is confined to the shores of 

 Patagonia and the Falkland Islands. 



The males of Serolis schythei differ from the females by their greater proportional and 

 actual breadth; the largest female specimen in the Challenger collection measures 32 mm. 

 in length by 32 mm. in greatest breadth, the largest male specimen measures 30 mm. in 

 length by 38 mm. in breadth. The greater breadth of the males is owing to the greater 

 length of the epimera. The sixth epimeron in this male specimen measures 17 mm. in 

 length, and extends for the space of about 5 mm. behind the extremity of the caudal 

 shield; in the female these epimera only measure 13 mm., and terminate just beyond 

 the end of the caudal shield. The first abdominal epimera also are longer in the male than 

 in the female ; the two sexes also difi'er, like many other species, in the shape of the 

 abdominal sterna. A third difference is to be found in the antennte, which are described 

 below. 



The colour of Serolis schythei (in alcohol) is pale brown, becoming darker in the 

 middle of the body, and diversified with dark brown or black spots, which vary considerably 

 in their number and size in different specimens. 



The cephalic shield is not unlike that of Serolis cornuta, Init the prominences and 

 ridges upon its surface are less developed ; there is a slight ridge dividing the antero- 

 lateral portions from the rest ; to the inside of and behind the eyes are two prominences 

 somewhat triangular in form, which correspond to those in Serolis cornuta, but are 

 directed more inwards ; between the two is a triangular area which forms the posterior 

 boundary, and owing to the comparatively sHght development of the lateral tubercles, 

 lies almost on the same level with them ; the disposition of these three prominences is 

 also like what occurs in Serolis newra, which in other respects shows considerable resem- 

 blances to this sj^ecies. The eyes are very large and prominent. 



Tliorax. — The thoracic epimera are flat and sickle-shaped ; as in Serolis cornuta the 

 external half of all the epimera projects freely ; the articular processes upon the epimera 

 are, however, entirely absent. The first epimera are divided by a transverse ridge. 

 While in the majority of species only the three anterior of the free thoracic segments are 

 divided by a distinct suture into a tergal and an epimeral portion, in Serolis schythei there 

 is also a suture separating the terga and epimera of the fourth segment. The j^osterior 

 margin of the tergura of each segment, with the exception of the first, is curved backwards 

 in the middle line into a short spine ; these gi^adually tliminish in size from before liack- 

 wards ; the antero-posterior diameter of the first free thoracic segment is a little less 

 than that of the succeeding segment, which is the laro;est, and measures 3 mm. in the 



(ZOOL. CHALL. EXP. — PART XXXIII. — 1884.) Kk 6 



