414 Rev. A. M. Norman on Acantholeberis, Lilljeborg. 



cisely similar circumstances to those under which the former 

 had been taken, among material collected in the Forge Dam at 

 Sedgefield, a spot about two and a half miles distant from the 

 first locality. It is from this example that the figures and 

 description of this paper have principally been derived. All 

 after-attempts (and they were not a few) to take this species in 

 the Forge Dam were as unavailing as they had proved in the 

 case of the colliery pond. 



We had at first thought that this abnormal species might be 

 new to science ; and when we found the description of this ani- 

 mal in Leydig's work, we could not help being amused at the 

 remarkable parallelism between our own experience and that of 

 Fischer and Leydig ; and we really are afraid that it was some 

 consolation, after the great trouble that had been taken in the 

 vain attempt to obtain additional specimens, that other natu- 

 ralists had suffered precisely similar disappointments. Fischer 

 says that he could only find a single specimen, and therefore is 

 obliged to content himself with referring to the description of 

 Lievin ; and Leydig writes, " I have only once observed Acan- 

 thocercus sordidus, in a muddy lake at Tubingen. It was a single 

 specimen, which struck me by its blood-red colour, and also by 

 the ample investiture of mud which surrounded the animal. 

 Added to that, it did not swim, but crept slowly along the bot- 

 tom of the vessel. Circumstances prevented my drawing the 

 animal, and every subsequent trouble I took to find the animal 

 again was in vain/' 



We have already referred to the fact that this species does not 

 appear to embrace all the characters which are assigned to the 

 genus Acantholeberis. It agrees with A. curvirostris in the 

 number of setse attached to the posterior antennas, and also in the 

 presence of setse of great length at the posterior ventral angle of 

 the carapace. It differs in the fact that the setse of the first two 

 joints of the lower branch of the posterior antennas are short, 

 and do not differ in character from the ordinary plumose setse of 

 the Daphniidse. But a more important instance of divergence 

 would appear to exist in the structure of the intestinal canal, 

 which does not seem to possess a loop near the excretory ori- 

 fice, as in A. curvirostris ; nevertheless a great dilatation of the 

 canal exists in an analogous position, forming apparently a 

 strong muscular rectum. At the same time, we speak with 

 hesitation on this point, and our opportunities of investigating 

 the structure of the species have not been sufficient to enable us 

 to speak with certainty on this and other points. 



Sedgefield, county Durham. 

 May 18, 1863. 



