780 Transactions of the Society. 



rotatoria. I made no accui'ate drawings of these at the time but 

 think probably they were the same. 



From these few remarks on the structure of HoJopedium it 

 will be seen that it differs in most important points from any other 

 Cladoceran in possessing a surrounding case of jelly, and in the 

 remarkable form of its second pair of antennas, though in other 

 points it closely resembles Sida. It has therefore been placed in 

 a separate family Holopedidae, which with the Sididae forms the 

 order Ctenopoda. 



Distribution. — In September 1881, I first discovered Holo- 

 pedium gibherum in Grasmere, in small quantities, but on return- 

 ing in the following May I found them in vast numbers, drawing 

 up as many as a solid tumbler-full after pulUng the net about 

 100 yards across the middle of the lake. In 3Iay I also found 

 them in Windermere in small quantities, but on again returning in 

 September I found no trace of them there whilst there were still 

 many in Grasmere. This time I found them in Easedale Tarn, 

 more than 900 feet above the sea. The water from this tarn runs 

 into Grasmere, and then on through Eydal Water to Windei-mere. 

 I was unable to ascertain whether they were present in Eydal 

 Water, as the proprietor of that lake being anxious to preserve his 

 fish and perhaps his Entomostraca, would not allow me to use his 

 boat. In September I dredged in most of the other lakes of 

 Cumberland and Westmoreland, but failed to find a trace of them 

 in any. This however cannot be taken as conclusive evidence as 

 1 failed to find them in Windermere at that time of the year. 



Bythotrephes Cederstromii Schodler (plate XII. figs. 1-8). 



This species (fig. 1) is closely allied to Fohjplienius 'pediculus. 

 The anterior portion of the head is almost entirely occupied by 

 the eye, a large pigment-mass surrounded by a number of long 

 transparent crystalline lenses. The brain, which lies closely 

 underneath the eye, is large, and composed of two parts. The 

 body is narrow, except for the brood-cavity, which is at the back, 

 'and is sometimes very large. 



'J'he most striking feature, however, of this Cladoceran is that it 

 possesses an extremely long spine at the end of its abdomen, more 

 than twice as long as the rest of the animal itself. At the base of 

 this spine is a pair of small spines standing out from it on a small 

 knob almost at right angles. The number of these spines varies 

 in different specimens, in some there is only one pair, in others 

 three. This is accounted for by the fact that the animal is not 

 always able to shed the covering of its long spine when it changes 



