12 U. S. BUREAU OF FISHERIES. 



Delavan, and Winnebao;o Lake, Wis. ; Omaha, Nebr. ; Urbana, Pekin, 

 Clifton, Havana, McHenry County, Meredosia Lake, and Lake 

 Michigan at South Chicago, 111. ; New Philadelphia and Tuscarawas 

 Eiver, Ohio ; Piney Branch, D. C. ; Point Pinellas, Fla. ; 'San Marcos, 

 Tex. ; Lake Merced, Fresno, Los Angeles, West Berkeley, and 'San 

 Francisco, Calif.; Yellowstone National Park; Volcan Reventado. 

 Costa Rica. 



Along with Eucrangonyx gracilis, Embody (1911) found it in the 

 cold water of trout brooks as well as the warmest waters of Ren wick 

 Marsh; also in Cayuga Lake, Fall Creek, and the inlet both above 

 and below the falls wherever there was any accumulation of living or 

 dead vegetation. He said that in spite of the drying up of the marsh, 

 the burning of the cat-tails and sedges, and the freezing of the 



ground to a depth of from 6 

 to 10 inches, both amphipods 

 appear each spring in the 

 usual large numbers in vari- 

 ous marsh pools. 



The largest Hyalella ob- 

 served by Embody measured 

 7.4 mm. (about 0.29 inch). 

 The average length of 26 

 breeding females was 5.46 mm. 

 Fi.;. 7.— Amphipod ; "scud;" "shrimp." (about 0.21 inch) . The small- 



fl^a?eJ/a fcmcA-erbocfceri. Enlarged 5 times. est egg-producing female 

 After Ward and Whipple. ^*^ i o ^/> / i ±_ 



measured 3.06 mm. (about 

 0.12 inch) and was 35 days old, producing 6 eggs. The average 

 number of eggs produced at one time by the females observed was 

 18, which number was repeated on an average of 15 times in 152 

 days, in the breeding season embracing the months of April to 

 September (April 2, 1910 — September, 1909). At this time the 

 temperature ranged from 7.8° to 30° C. (33.4° to 86° F.) with an 

 average of 20.14° C. (68.252° F.) in 26 readings. Observation 

 upon individuals gave the period from oviposition to the date of 

 hatching as 8.5 and 8 days, the average temperature being 23.6° to 

 24° C. (74.48° and 75.2° F.), respectively, in July. The young re- 

 mained in the brood pouch on an average of 2 days. The total 

 reproductive capacity of one pair and its progeny in the period of 

 152 days was 13,976 in 4 generations. In 180 days from hatching, the 

 young' grew from 1.27 mm. to 6.4 mm. (0.05 to about 0.25 inch) in 

 length. 



Eucrangonyx gracilis. — Several species of Eucrangonyx are com- 

 paratively common in different parts of the countr3\ The U. S. 

 National'Museum records (1907) are: Providence, R. 1.; Ann Arbor, 

 Mich. ; Isle Royal, Lake Superior ; Portage, Wis. ; Champaign, 111. ; 

 Irvington, Ind. ; Delaware, Ohio ; Nashville, Tenn. 



Ortmann (1918) says they live in ponds, springs, and wells. Em- 

 body (1911) indicated that '£". gracilis like Hyalella, with which he 

 found it associated, was common under extreme conditions and varia- 

 tions of temperature from cold spring brooks to warm stagnant 

 marshes. Its habitat seems to be indentical with that of Hyalella 

 knickerhocheri, and both it and Hyalella seemed to be unaffected by 

 the freezing of the marsh to 6 or 10 inches, or the burning of the cat- 

 tails and sedges. 



