Cyclops. 
215 
Cyclops serrulatus Fischer. 
Plate VI, figs. 2-5. 
1838. 
1851. 
1853. 
1857. 
1863. 
1863. 
1863. 
1870. 
1872. 
1875. 
1878. 
1880. 
1882. 
1883. 
1884. 
1885. 
1886. 
1891. 
1891. 
1891. 
1892. 
C. agilis Koch (3), H 21, pi. III. 
“ serrulatus Fischer (5), p. 423, pi. X, figs. 22, 26-31. 
Lilljeborg (6), p. 158, pi. XV, fig. 12. 
Claus (7), p. 36, figs. 1-3. 
Sars (11), p. 45. 
Claus (9), p. 101, pi. I, figs. 1 and 2; pi. 
IV, fig. 12; pi. XI, fig. 3. 
Lubbock (10), p. 197. 
Heller (12), p. 6. 
Fric (13), p. 222, fig. 18. 
Uljanin (15), p. 34, pi. VIII, figs. 1-8. 
Brady (18), p. 109, pi. XXII, figs. 1-14. 
“ agilis Rehberg (19), p. 545. 
“ serrulatus Herrick (23), p. 230. 
“ pectinifer Cragin (24), p. 6, pi. IV, figs. 1-7. 
“ serrulatus Herrick (26), p. 157, pi. O, figs. 17-19. 
“ agilis Daday (27), p. 240. 
“ agilis Vosseler (28), p. 190, pi. V, figs. 29-31. 
“ serrulatus Schmeil (37),. p. 29. 
Brady (36), p. 18, pi. VII, fig. 1. 
Richard (39), p. 234, pi. VI, fig. 19. 
Schmeil (41), p. 141, pi. V, figs. 6-12. 
C. serrulatus is found everywhere. It is the most common of 
all the species of Cyclops. In the larger bodies of water it is 
more common in littoral collections, but it occurs not infre¬ 
quently in pelagic collections. 
This species has a wide limit of variation, the extreme forms 
differing so much that one is at first inclined to rank them as 
separate species. At one extreme is the form common in ditches, 
pools, and littoral collections, which seems to correspond nearly 
to montanus Brady. It averages .85 mm m length; the furca 
is not quite as long as the last two abdominal segments, and 
the external terminal seta is transformed into a stout spine 
