[ronus ignavus Bastian. 
PI. IV. tig. 83. 
1865. Bastian, p. 104. PI. IX. fig. 34a—b. 
1876. Butschli, p. 384. T. XXV. fig. 15 a—e. 
1884. de Man, p. 70. T. X. fig. 40. 
This species occurs rather abundantly in the Dyrehaven near 
the Fuglesangsø. It lives here in black mud and damp mould 
where it would be almost impossible to find it, if it had not the 
same peculiarity as the Mononchs. namely to swim on the surface 
of the water. If some mud is spread in a flat glasscup and water 
is poured over it the animals will mount to the surface where they 
can be easily collected by help of a needle. Later the species has 
been taken at the Furesø together with Dorylaimus stagnalis and 
Trilobus gracilis, just the same species among which Butschli has 
collected it in the river of Main. The female organ, the character- 
istic ring-musculature of which is discussed both by Butschli 
and de Man, I have taken the opportunity to figure. The dimen¬ 
sions of the Danish specimens agree principally with those from the 
river of Main. 
I note the measurements of a female of middle size: 
Zeiss Okular mikrom. A. O c. 2. 
Length 213 = 3,4 mm. 
Oes. 39. 
Vulva 111. 
Tail 13. 
Width 4. 
Phar. cavitv 7 1 /2. 
The formula of de Man gives: a = 53, /9 = 5 1 / 2 . ^ = 16. 
Ironus longicamlatus de Man. 
1884. de Man, p. 71. T. XXXIV. fig. 140. 
The 7. longicaudatus occurs at localities much resembling 
those in which 7. ignavus lives; it has f. i. been taken in mud 
from the Fuglesangssø in Dyrehaven. Further it has been collected 
