AKTD OTHEB BRITISH PRAWNS. 



123 



spines (text-fig. 6 A, B) In JSTorfolk specimens (text-fig. 6C) the 

 appendix is always very much shortei' than the inner branch of 

 the pleopod, and is provided with a row of spines along the inner 

 and anterior side. This diflference is very striking, and easily 

 seen without dissection. 



(2) The short flagellum of the antennule is almost or quite as 

 long as the peduncle, and the free part is nearly half as long as 

 the fused part. 



Table III, 



Comparison of measurements of Norfolk and Algerian 

 specimens of P. varians. 



Second Leg. 



Norfolk, $ 



; ? 



Algeria, S ■ 



„ <?. 

 » ?• 



O 



100 250 

 „ i269 



„ i267 



I 



„ 1295 



150 i 325 



169 

 167 



331 

 329 



195 368 



264 

 254 

 236 



280 



Antennule. 



100 62 



45 



17 



In all the specimens, male or female, there are either three or 

 four feathered setse on the telson. 



I have not been able to examine any representatives of the 

 South European fresh- water form, and, so far as I know, no 

 attention has previously been paid to these two characters of the 

 male, so that it is possible they may be found to be distinctive 

 not of var. mesogenitor alone, but also of var. macrogenitor . I 

 consider them of such importance as to justify the separation of 

 the Algei'ian form as a distinct species, which, if it should prove 

 to be identical with the Tunisian form and not to share its 

 characters with var. macrogenitor, should take the name P. meso- 

 genitor SoUaud *. 



* Since the above was written M. E. Chevreux has been good enough to send me 

 specimens of P. varians from Lake fetzara in Algeria, but unfortunately they 

 proved all to be females. I have also, through the kindness of Dr. W. T. Caiman, 

 been able to examine specimens of the var. macrogenitor from several localities in 

 south Europe and find that the appeiidix masculina does not difler from that of the 

 brackish-water variety. 



