150 
PuLses OF ANURZA COCHLEARIS. 



























Year Date Temp. No. Date Temp. No. Date Temp. No. 
1894 — = June 12 78° 1,344 ae 
1895 | Apr.29| 64° 180,480 July 18 | 80° 17,805 
1896 | May 8 76° 100,870 June 11 a> 95,200 july 2 81° 12,800 
‘ S 28 81° 17,600 
1897 | May25 66° 620,800 July 21 82° 37,600 
1898 | May10|] 62° | 1,145,600] June 21 77° | 372,800 | July 19 g4° 17,200 
Year Date Temp. No. Date Temp. No. Date Temp. No. 
1894 Sept. 4 78° Ueno) 
1895 | Aug. 21 83° 17,805 Sept. 23 io ue ay al Nov. 20 44° 1120 
1896 | Aug. 21 79° 5,600 Sept. 16 (pal 6,224 Dec. 29 B52 3,840 
1897 | Aug. 24 78° 45 ,600 Octs, 5 70° 4,800 
1898 | ———— | ———— ——— Sept. 27 ie 54,400 Nov. 21 40° 10,000 
Oct 2'5 48° 28,500 : 




conditions seem thus to be found in the river at temperatures some- 
what below the maximum, between 60° and 70°. 
The phenomena of recurrent pulses are distinctly traceable in the 
seasonal distribution of this species, not only in 1898 (Table I) but 
also in preceding years. The large May and June pulses of 1898 
appear on the declines of the spring and the June rise, respectively ; 
the pulse of September 27 is in a falling river; and that of October 
25; on_a-slowly rising flood (Pt..1., Pl XU). Inviso7 (ec eer 
XI.) the first two pulses attend the spring flood and June rise in like 
manner, but the two subsequent pulses are in stable low water. In 
1896 five of the seven pulses lie on the declines of the recurrent 
floods of that year and two in rising waters (cf. Pl. X. of Pt. I. and 
the table just given). In 1894 and 1895 the pulses appear either - 
in falling water or in the earliest stages of the rise. The number of 
pulses on declining waters is somewhat greater than the relative 
number of days of this condition would lead us to expect, and it 
seems probable that optimum conditions for the appearance of 
larger numbers of Anurea cochlearis are to be found in such hydro- 
graphic conditions. The run-off of impounded backwaters is one 
of the favorable phases during flood decline. On the other hand. 
wet 
“ED was 
