FRESH WATER CYCLOPID.T; AND CALANID.l';. 



109 



(1891), when ho found the filter-bods of the marine baths at 

 Bootle — close to the first-mentioned locality — swarming with it. 



Gentjs ACAETIA, Dana. 

 1. Acartia longiremis, Lilljeborg (PI. XIV., figs. 1-4). 



1853. Dias longiremis, Lilljeborg (9), p. 181, pi. XXIV., 



figs. 1-13. 

 1863. ,, ,, Claus (18), p. 193, pi. XXXIII., 



figs. 6-14. 

 1878. ,, ,, Brady (32), p. 51, pi. V. 



1881. ,, ,, Giesbrecht (37\ p. 146 ; ?V^m (35), 



p. 3. 

 1881. ,, hifilosus, Giesbrecht (37), p. 147 ; idem (35), p. 3. 

 1881. ,, ? discaudatus, Giesbrecht (37), p. 148; idem (35), 



p. 3. 

 1887. „ ? ,, I. C. Thompson (50b), p. 36, pi. V., 



figs. 1-6. 

 1890. ,, longiremis, Bourne (64), p. 147, pi. XI., figs. 4-6. 



It has been proposed by Dr. "W. Giesbrecht to break up the 

 forms hitherto considered as belonging to Dias longiremis, Lill- 

 jeborg, into two, or perhaps three, distinct species : — D. longiremis 

 (restricted form), D. hifilosus, Giesbrecht, and D. discaudatus, 

 Giesbrecht. The last-named may or may not be considered as 

 having been previously included under the old term longiremis. 

 The characters relied upon by Giesbrecht to uphold this separa- 

 tion are as follows : — 





longiremis. 



hifilosus. 



discaudatus. 



Frontal filaments 



absent 



two 



absent 



Last thoracic seg- 

 ment 



armed with two 

 large & several 

 smaller spines 



unarmed 



unarmed 



Furca 



long 



short 



short and (in the 

 female) dilated 



Fifth pair of feet 

 (male) 



Fifth pair of feet 

 (female) 



small 



large 



large 

 small 



veiy large 

 very small 



To me it appears that these characters — trivial even when 

 displayed to the best advantage on paper — are of even less ac- 

 count when put to a practical test, their inconstancy even more 

 than their intrinsic triviality being fatal to their acceptance as 



