202 Prof. C. Chilton on AscUus aquaticns. 



external cliaracters unless one lias fully adult and perfect 

 malrs wlien tliey nii'o^lit be clistingnislied by the lenp;tli of the 

 second antenna? and by fbe shape of the lateral margins of 

 sepfments 2 to 5 of the person. Many of my specimens are 

 immature and in others the antennaB are broken off, and, 

 thoiifrh the Tunbridge Wells specimens showed the lateral 

 margins of the ])era?on segments as described by Racovitza, 

 the difference from the other specimens was hardly sufficient 

 to be distijictive by itself. 



The following are brief notes on the specimens I have 

 examined. In the female from Edinburgh the inner lobe 

 of the first maxilla showed the four seta? characteristic of 

 j4. aqunticiis on the one side, while the appendage on the 

 other side had only three* ; the second pleopod is circular in 

 outline ; the male examined from Edinburgh is evidently not 

 fully mature, for the first thoracic leg has the propod only 

 slightly triangular, though it is certainly approaching]^ towards 

 the outline represented in Racovilza's figure ; in the fourth 

 leg the row of spinules on the carpus is distinctly discon- 

 tinuous and contains only a few sjiines; the first and second 

 pleopods show the characters described by Racovitza, the 

 exterior margin of the exopod of f)leopod 1 being distinctly 

 emarginate. 



In a male specimen of AseUufi orpinticiis, Linne, from the 

 River Neckar the first and fourth pairs of le,<;s correspond, 

 on the whole, well with Racovitza's figures and descriptions, 

 though the first one is not fully developed, and consequently 

 the propod not so distinctly triangular ; the first and 

 second pleopods are in close agreement with Racovitza's 

 description, the emargination on the external border of the 

 exopod being quite distinct. 



Racovitza has examined and identified specimens of 

 AfteUns .arjuafiru.i, Ijium?, from " Askam bog (Yorkshire), 

 Birmingham/' from various localities in France, and from 

 Carniola (Adelsberg), while on the testimony of other authors 

 he records it from Norway, Poland, Livonia, Russia, Germany, 

 Switzerland, and Greenland. The species is therefore very 

 widely distributed. It is this s])ecies that has been so well 

 described and figured by Sarsf. 



* ProbaMy furllier fxaniiiintion would sliow that the oral appondnpes 

 in AHelliis are linldc to a onnsidcrablo anionnt of variatioi), as lias been 

 pliown by l>r. Colliiipc to ('.\itil in the Onifcoidea or Terrestrial I.«opoda 

 (Journ. i^inn. Soc, Zool. vol. xxxii. (1914) pp. 287 293, pis. xx., xxi.j. 



t 1867, ' Hist. nat. dos Crustart's d'oau douce de Norvepe,' p. 93, 

 "plfl. viii., ix., i*v: x. ; and 1S97, 'Crustacea of Norway.' vol. ii. ]>. 97, 

 ]il. xx.xix. 



