358 Mr. R. Gurney on certain 
brevicornis (Van Douwe). It occurs in these stems in fair 
numbers, and can generally be distinguished from N. hider- 
nica, with which it is associated, by its smaller size and 
absence of brown markings. ‘his distinction in colour 
does not always hold good, since, on the one hand, Van 
Douwe notes strong pigmentation in his examples, and, 
on the other hand, N. hibernica may sometimes be quite 
colourless. Structurally N. simplex is most closely allied to 
N. spinipes, Boeck *, but differs from it in the structure of 
the first and fifth feet and of the prehensile antenna of the 
male. The penultimate joint of the latter in N. simplex has 
a series of small knobs along its inner edge, which are not 
found in any other species of the genus. In some males 
of N. hibernica this joint has a few cuticular ridges, which 
indicate an approach to the condition found in N. simplex. 
Nitocra simplex appears to be confined to waters in which 
there is an appreciable quantity of salt present. Schmeil 
found it in Holstein, in water having a salinity of °5°/,, 
while Thienemann + records its occurrence in water with a 
salt content of about 2°5 grm. per litre. In Hickling andin 
Horsey Mere the salinity varies between 40 and 70 grains 
per gallon. I have found specimens in a collection made in 
1899 at Cley, in Norfolk, in a ditch close to the sea in which 
the water was probably slightly brackish, though it contained 
otherwise only freshwater Entomostraca. 
The genus Nitocra seems to be characteristically marine, 
and N. simplex holds an intermediate position between such 
species as N. spinipes which is found only in water of high 
salinity and N. hibernica which is a genuine freshwater 
species. 
5. Mesochra rapiens (Schmeil). 
Apsteinia rapiens, Schmeil, Zeits. Naturw. Ixvii. 1894, p. 348. 
Canthocamptus hirticornis, Scott, 18th Ann. Rep. Scottish F. B. 1895, 
p- 261. 
Canthocamptus megalops, Lilljeborg, K. Sy.-Ak. Handl. xxxvi. 1902, 
. 30, 
Apsteinia rapiens, Van Douwe, Deutsch. Susswasserfauna, 1909, p. 61. 
Mesochra hirticornis, Sars, Crust. of Norway, v. 1911, p. 210. 
The identity of C. megalops, Lillj., with Mesochra hirticornis °* 
has already been pointed out by Dr. Scott and accepted by 
Prof. Sars, but a comparison of the description of Schmeil 
and the figures given by Van Douwe of Apsteinia rapiens 
* T refer to N. spinipes, as described by Sars (Crust. of Norway, v. 
p. 218). With this species NV. palustris (Brady) is synonymous. 
+ Verh. Deutsch. Zool. Ges, Vers, xxiii. 1913, 
