160 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
When the lower divisions of the trough contain hatching eggs and fry that can 
not readily be removed without injury, the first or upper division (in which nearly 
all the hydras will have fixed themselves) may be cleaned by shutting off the supply 
pipes, placing a temporary partition between the upper and lower divisions, and, 
after a brisk scrubbing, quickly siphoning off the water and floating hydras from the 
upper division of the trough. 
As the water now entering the hatchery is taken from Rock Creek and from the 
spring, both of which are free from hydras, it is probable that loss from this cause 
will cease as soon as all the hjulras now in the hatching troughs and supply pipes can 
be removed. 
It was impossible to find characters other than those of color and size by which 
to differentiate this hydra specifically from the well-known II. fusca Linnaeus. It 
differs from that common form only in being of larger size and in the entire absence 
of coloration. Among the large number of individuals observed, both in the troughs 
of the hatchery and at the lake, not one showed a trace of fuscous coloration. These 
differences appear to be constant, and I propose the n^mo, pallida for the new species, 
in allusion to its lack of color. It may be described as follows: 
Hydra pallida Beardsley, new species. 
Characters . — Body cylindrical, 1 to 2 cm. in length and .15 to .30 mm. in diameter; tentacles 5 or 6, 
when fully extended two or three times as long as the body; color, milk-white in reflected light, 
whitish and translucent in transmitted light. 
Differs from typical Hydra fusca in being somewhat larger in average size and in the entire absence 
of fuscous coloration. 
Type locality . — United States fish-cultural station, Leaclville, Colorado. 
