FRESH-WATER CrCLOPID^ AND CALAXIDJE. 7 



1863. Cyclops tenuicornis, Lubbock 19), p. 202. 

 1872. ,, „ Eric. (24), p. 219, fig. 12. 



1875. „ Clausii, Poggenpol (26), p. 70, pi. XY., 



figs. 4-11. 



1875. „ tenuicornis, Uljanin (28), p. 30, pi. IX., 



figs. 12, 13. 



1876. „ ,, Hoek(29).p.l2,pl.IIL, figs.1-11. 

 1878. „ ,, Brady (32), p. 102, pi. XVIIL, 



figs. 1-10. 



1883. ,, ,, Cragin (40), p. 3, pi. II., figs. 1-14. 



1884. „ ,, Herrick (41), p. 153, pi. R., fig. 16. 



1885. „ „ Daday (44), p. 211. 



1886. „ „ Yosseler (46a), p. 189, pi. IV., 



figs. 6-10. 



Herrick, in his " Final Report on the Crustacea of Minnesota," 

 expresses the opinion that the two forms known under the names 

 signatus or coronatus and tenuicornis represent but different stages 

 of development of the same species. In this opinion, after an 

 examination of all the material at my disposal, I am disposed to 

 agree, though until the actual course of development has been 

 watched in artificially bred specimens, one cannot be quite cer- 

 tain. The serrated edges of some of the joints, and the serrated 

 rib on the last joint of the antenna, in the signatus form, seem 

 to represent the ultimate, as the smooth joints and rib represent 

 the penultimate {tenuicornis*) stage of growth. The pectinate 

 armature of the second joint of the antenna, which I have figured 

 in the Ray Society Monograph as a character of C. signatus, I 

 find to occur also in C. tenuicornis. Nor can the frequent pre- 

 sence of ovisacs in C. tenuicornis be held certainly to indicate 

 the maturity of the individual, parthenogenesis being so fre- 

 quent a phenomenon amongst the Entomostraca. 



This species, in both its forms, is widely distributed : it is in 

 fact one of the commonest species, not only in the British 

 Islands but on the Continent of Europe and in North America, 

 having been recorded as occurring in Scandinavia (Sars), Ger- 

 many (Claus, Rehberg, &c), Bohemia (Eric), Tyrol (Heller), 

 Erance (Richard), Holland (Hoek), America (Herrick). In Great 

 Britain, both forms of the species are very common and con- 

 stantly occur together, as indeed they must necessarily do if the 

 view of their relationship here adopted be correct. 



72 



