hnoion as Asellus nqnaticus. 



201 



altlioiif^li tlie animal lias bepii fully ilesciihed and fi<rure(l hy 

 various uutliors, no one until recently appears to have suspectfil 

 that the indiviiluals l)elon<;etl to more than one form or .sps-cics. 

 In a recent j)aper, however, Monsieur E. G. Itacovitza * lias 

 pointed out that under the name Asellus aquaticus two quite 

 distinct forms or series of forms have been confused, and that 

 these differ distinctly from one another by several fairly wo'l- 

 niarked characters, ile adopts the name Asellus uguaticus, 

 Linnd, 1758, for one species which appears to be the com- 

 monest and tiie only one hitherto fully described and figured ; 

 for the other, which is therefore new, he suggests the name 

 Asellus meridianus. For a full account of the differences 

 between tiiese two and for excellent figures showing them 

 reference should be made to ]\I. Racovilza's paper. It seem^ 

 desirable, hoAvever, to call the attention of English naturalists 

 to his results, and in doing so it will be sufficient to indicate 

 briefly some of the more important differences. They are as 

 follows : — 



A. aquaticus. A. meridianus. 



Antetina 2 . . Male almost as long as body, Two-thirds length of body 



female a little shorter. in both sexea. 



Maxilla 1 . . J'^oiir \)\ninose seix on distal J'nv plumose setie on distal 



margin of inner lobe. margin of inner lobe. 



I'erceupod 1 . Adult male with large tri- Inferior margin of projiod 



angular ])rojectiou on in- almost straight, no pro- 



ferior margin of propod. jection. 



Pereeopud i . Carpus with lougitudiual Carpus with row of 10-12 



row of 4-5 spines, discou- long spines, continuous, 



tinuous. 



Pleopod 1 of Exterior margin of exopod Exterior margin of exopod 



male. 



eniargiuate. 



strait^ht. 



Besides these there are other minor differences in the shaj)o 

 of the lateral margins of the peraoii segments II. to V. and 

 in the second pleopods of both male and feiUMle animals. 



On receipt of M. Ivacovilza's paper I exannned tlie speei- 

 niens in my own collection, and find tiiat both forms are 

 represented — namely, Aatllus aquaticus, nuujcrous specimens 

 collected in the Ediuburgli-Gila.sgow Cai,ul at JOdiiiburuh 

 al)out the year IHIOS, others in tiie Uiver iS'eid<ar, 1 Kidelbi ig, 

 22. iv. IDOO; Asellus lueriilianus, several .specimens trom a 

 small brook at Tunbiidge Wells, Kngland, f'oi warded to nie 

 by the Uev. T. H. li. lStebi)ing. I have di.-isicled and ex- 

 aniined a nuile and a female from each of these localities, as 

 it is almost impossible to distinguish the two species by 



* Arciiiv. Zool. Exper. et (len. 1919, tome 58, Notes el Kevue, 

 pp. 31-i;i. 



Anu. cC- Ma<j. N. Hint. Ser. '.•. \\>l. v. II 



