278 DISCOVERY REPORTS 



when maturity is reached the lamellae are fully formed, and a moult occurs after each 

 brood is hatched. The brood-lamellae are fully formed at each moult and immediately a 

 new brood is reared. 



The fact that female Serolids with the narrow type of brood plate are comparatively 

 rare, seems to suggest that those present are immature specimens rather than mature 

 females in the non-breeding phase, and that, as in Gammarus, once maturity is reached, 

 the brood-lamellae are fully formed after each moult and a new brood is reared. It 

 would be interesting to know how far these two breeding methods are characteristic of 

 fresh water and salt water respectively. 



Nordenstam (1933) has deah with "the scales and setae in the family SeroHdae" 

 (pp. 14-38) in great detail: many of the types described by him are considered in the 

 present paper under the various descriptions of species. 



KEY TO ALL KNOWN SPECIES OF SEROLIS. 



A. Small dorso-lateral portions of the tergum and of the coxal plates of the eighth thoracic somite 

 present. Endopod of the uropod absent. All free thoracic somites (3rd-8th) separated from their 

 coxal plates by sutures. Hindmost suture of seventh thoracic somite complete. 



I. Dorsal surface of head and body strongly sculptured; terminal segment studded with 



tubercles 1. S. beddardi,Cz\mAn. 



II. Dorsal surface of head and body segments nearly smooth; terminal segment smooth except 



for a median and a pair of sub-marginal ridges 2. S. !atifrotis,MVhite. 



B. Tergum and coxal plates of the eighth thoracic somite absent. Both endopod and exopod of the 

 uropod usually present. 



I. Tergum of seventh thoracic somite articulating freely with that of the first abdominal segment, 

 that is, the hindmost suture of the seventh somite is complete. 



A. All free thoracic somites (3rd-7th) separated from their coxal plates by sutures ; eyes small 



and inconspicuous 3. 5. ^ran&, Beddard. 



B. Only the first four free thoracic somites (3rd-6th) separated from their coxal plates by 

 sutures. 



I. Coxal plates of seventh thoracic somite extend backwards to about the middle of the 

 terminal segment, pleural plates of second and third abdominal segments short, not 

 extending far beyond the anterior margin of the terminal segment 4. S.paradoxa, Fabricius. 



II. Coxal plates of seventh thoracic somite extend backwards, in the male, for some 

 distance beyond the posterior extremity of the terminal segment; pleural plates of 

 second abdominal segment long, extending beyond the posterior extremity of the 

 terminal segment, those of the third segment short 5. S. schythei, Liitken." 



III. Coxal plates of seventh thoracic somite extend to the postero-lateral angles of the 

 terminal segment, but not as far as the pleural plates of the second abdominal segment; 

 those of the third segment extend backwards to about the middle of the terminal 

 segment 6. 5. /)o/«m, Richardson. 



1 5. serrei, Lucas, has not been recorded since first briefly described in 1877 and is possibly identical with 

 S. schythei. 



