D. J. SCOURFIELD ON THE WINTER Ef4G OP A RARE WATER-FLEA. 173 



The first specimen of Leydigia acciyithocercoides seen by me 

 was in the condition shown in Fig. 1 (PI. 11). It was found in 

 October last, in sediment collected from the bottom of Barton 

 Broad, Norfolk, at the end of September. The animal, which 

 was dead when found, had apparently attempted to moult, but 

 had only been partially successful. It was evident at once, by 

 the dark colour of the dorsal part of the shell, that a proto- 

 ephippium, having an outline strikingly similar to that of the 

 ephippia of some species of Daphnidse, had been produced ; and I 

 further noticed, but without at first realising its significance, that 

 the entire free margins of the valves were darkened almost to the 

 same extent as the proto-ephippium. 



Closer inspection soon revealed several other curious facts. 

 For instance, it was noticed that the ventral margin of the 

 darkened dorsal area constituting the proto-ephippium was 

 marked by a line of approximately rectangular cells which were 

 only loosely attached in their places. A highly magnified view of 

 the anterior part of this line is shown in Fig. 2. On the left is 

 a corner of the proto-ephippium, the anterior margin of which 

 is formed, as is usually, if not always the case, by the line of 

 junction between the head-shield and the valve. On the right, 

 above, is a portion of the darkened and possibly thickened free 

 anterior margin of the valve ; while below this the unmodified 

 part of the valve is indicated by the fine striae on its surface. 

 Some of the anterior cells of the boundary line have already 

 fallen out ; others are quite loose, as is shown by their positions. 

 These cells seemed to be quite free from markings of any sort, 

 although the surface of the head and valves in this species is 

 covered with extremely minute and closely-set striae, just as in 

 Alona ciffinis. The special function of this line of loosely con- 

 nected cells is evidently to allow of the easy separation of the 

 proto-ephippium from the unmodified part of the valves. 



The next peculiarity observed was that the line of cells above 

 referred to was not limited to bounding the ventral margin of 

 the proto-ephippium, but was continued completely round the 

 free edges of the valves just within the darkened margins. This 

 gave the clue at once to the meaning of the modified valve 

 margins. If the shell had been completely moulted they would 

 no doubt have broken away from the unmodified parts of the 

 valves, and, remaining attached to the proto-ephippium, would 



