3.')8 Mr. H. Giini^^v nn certain 



brei^icornis (Van Ponwe). It onciirs in these stems in fair 

 numbers, an(i can generally he distingnished from X. hiber. 

 iiica, with which it is associated, by its smaller size and 

 absence of brown marUings. 'I'liis distinction in colonr 

 does not always ii')l(l good, since, on the one hand, Van 

 Douwe notes strong pigmentation in his examples, and, 

 on the other hand, .V. Idhfrnicn mav so-netimes be quite 

 colourless. Structurally N. siinip/c.r is most closely allied to 

 A^. .ynnipes, 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. simp/e.r lias 

 a series of small knobs along its inner edge, which are not 

 found in any other species of tlie 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 he confined to waters in which 

 there is an apprecial)le (piantity of salt present. ISclimeil 

 found it in Holstein, in water having a salinity of 'o^/^, 

 while Thienemann t records its occurrence in water with a 

 salt content of about 2'5 grm. per litre. In Ilicklin*; and in 

 Horsey !Mere the salinity varies between 40 aiul 70 lirains 

 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 biackish, though it contained 

 otherwise only freshwater Eiitomostraca. 



The genus Nitocra seems to be characteristically marine, 

 and N. simplex liolds an interuiediate position between such 

 species as X. spinipes which is found only in water of high 

 salinity and N. hibirnica which is a genuine freshwater 

 species. 



5. Mesochra rapiens (Schmeil). 



Apgleiuid rapiens, Schmeil, Zeils. Xalurw. Ixvii. 1894, p. 348. 

 Canthocamptus lu'rfieorriis, Scott, 18tli Ann. Kep. Scottish F. D. Isft.'i, 



p. 251. 

 Canthocnmptus mcyulops, Liiljoborg, K. Sv.-Ak. I land). xx.xvi. li'ti'J, 



p. .".0. 

 Apsteinia rapiitis, Van Doinve, Deiitsch. Susswfl.«seifniinn, 1900, p. Gl. 

 Mesochra liirticonns, Sars, Crust, of Norway, v, 1911, p. I-'IO. 



The identity of C. megolops, Lillj,, with Mesochra hirtimniis 

 has already been pointed out by Dr. Scott and accejited by 

 i'rof. Sars, but a comparison of the description of JSchmcil 

 and the figures given by Van Douwe of Apslcivia rapiens 



* I refer to N. spinipes, aa described bv Snrs (Crust, of Norway, v. 

 p. 21 H). With tliie 8i)eiips A', pulustris (liiudy) is syuonyniuus. 

 t Verb. Deutscb. Zotil. (ie.s. ^'ers. x.viii. 191o. 



