MU. R. GURNET ON FRESH- AND BRACKISH-WATER CRUSTACEA. 641 
Daphnia uacustris, Leydig. South Walsham, Ormesby and 
Kollesby Broads, and Fritton Lake. A single 
record from Barton Broad. 
,, cucullata, Sars. Abundant in all the open Broads 
except the Hickling group, and taken occasionally 
at Sutton and Barton. It does not seem to occur at 
all in the Yare or its Broads. 
Scapholeberis mucronata, O. F. Muller. The typical form of 
this species is very rare, and only occurs late in the 
year. 
,, aurita (S. Fischer). This is a new record for 
the British Isles, for which I am in the first 
instance indebted to Mr. R. A. Todd, who found 
it in a pond at Herringfleet. Curiously enough 
both he and I, myself, had collected in this same 
pond before without discovering it, and it practically 
disappeared very shortly after. Such cases of sudden 
appearance and disappearance of conspicuous species 
may perhaps be explained, as has been suggested by 
Mr. Scou rfield, by the assumption that the species 
has been introduced by birds, but has found the 
conditions unsuitable for a permanent home. I have 
since found S. aurita in a ditch at South Walsham, 
and also in Catfield Fen. Like the preceding 
species it has the habit of swimming on its back 
supported by the surface film, but this suspension 
seems to be effected by means of a series of minute 
teeth disposed along the flattened ventral margin of 
the shell valves, and not by modified setae as in 
«S. mucronata. 
Simocephalus vetulus (0. F. Muller). 
,, exspinosus (Koch). Somerleyton, Smallburgh, 
Blundeston, and Sutton. A rare species, found 
only, in my experience, in ponds and small 
ditches. 
Ceriodaphnia reticulata (Jurine). Generally in small waters 
only. The variety serrata, Sars, occurs fairly 
frequently. 
MEGAL0P8. Sars. 
