Copepod Fauna of the "Maare " of the Eifel. 297 



the basal joint. In the last quarter of it, on tlie outer 

 margin, is seated a spine wliich is as long as the joint. 

 At the apex is geniculated a spine formed by the transfor- 

 mation of the third joint of the ramus, which is at least as 

 long as the three preceding joints. At its base it is dilated 

 into a vesicular form, and about the middle it makes a 

 bend, so that its two halves stand nearly at right angles 

 to each other. The one-jointed inner ramus bears some 

 fine hairs at the extremity. The left rudimentary foot of 

 tlie male is a little shorter than the right one. The basal 

 joint is larger than that of the right foot. The apex of the 

 second joint is produced into a short stiff spine, close to which, 

 on tlie inside, another more slender one is attached. In the 

 small ovisac I always found only two eggs. The length of 

 the female including the caudal seta? is 1 millim. and that of 

 the male 0'8-0*9 millim., or rather less than found by Lillje- 

 borg. _ _ 



This species comes very near Diaptomus gracilis^ Sars, and 

 it is quite possible that it is only a form of that species pro- 

 duced by adaptation and isolation. 1 have obtained, also from 

 Dr. Zacharias, an abundance of Diaptomus gracilis from the 

 " Faulen See," near Frankfort on the Oder. Some of the 

 specimens of normal size showed small variations which 

 partly agree with the characters of Diaptomus graciloides. I 

 hope shortly to be able to make a more exact investigation of 

 these conditions, by which, perhaps, some light may be 

 thrown upon the causes of the variations. Diaptomus gracil- 

 oides was found by Lilljeborg chiefly in the great freshwater 

 lakes of Sweden and the Russian Kola peninsula to near the 

 shores of the northern icy sea. 



Of all the species cited from the " Gemiindcr Maar" I 

 obtained only very few sexually mature animals, and espe- 

 cially in the case of the Diapitomus I had much trouble in 

 finding in the rich material a sufficient number of adult speci- 

 mens for the investigation. 



All the Copepoda were strongly coloured red, the Diap- 

 tomus most intensely. The colouring-matter was chieHy 

 combined with fat and could be extracted with this by ether. 



The group of the Copepoda inhabiting the 



HI. HOLZMAAR 



is again differently constituted from that in the fauna of the 

 two '' Maare " described. There are still tlie three Cyclopidse 

 found in all the " Maare " : — 



