78 Wisconsin Academy of Sciences, Arts and Letters . 
shorter than the inner, armed with three terminal spines and 
a single spine on the upper margin. Third uropods with h 
short, thick peduncle devoid of spines; the single small ramus 
less than half the length of the peduncle and armed with three 
spines at the tip. 
Telson about twice as long as wide, subrectangular but 
slightly narrowed distally, the posterior margin with a slight 
emargination on either side of which is a cluster of four or five 
spines. 
Length, 5 millimeters. All the specimens were entirely de¬ 
void of pigment. The gnathopods do not present any marked 
differences in the two sexes. 
This species differs from Crangonyx tenuis Smith from Con¬ 
necticut in having considerably longer rami in the first uropods, 
in having the outer ramus of the second uropods but little 
shorter than the inner, instead of half as long, and in having a 
much shorter flagellum in the second antennae. It is more 
closely allied to (7. vitreus (Cope) from Mammoth Cave, Ken¬ 
tucky, so much so that I was at first somewhat in doubt of its 
specific distinctness. Through the kindness of Mr. Kichard 
Ratkbun, who sent me some specimens of the latter from the 
United States National Museum, I was enabled to compare the 
two species and to assure myself that they are really different. 
In C. putealis, the first gnathopods are considerably stouter 
than in vitreus , the hand is more widened distally and has no 
setae on the posterior margin; the hand of the second gnatho¬ 
pods has the palm more oblique, and a shorter posterior mar¬ 
gin which is devoid of setae except near the palm; the first 
uropods have fewer spines on the upper margin of the peduncle, 
and the telson is relatively longer, being nearly twice as long 
as wide, whereas in C. vitreus its width nearly equals its length. 
Camera drawings of parts of C. vitreus are inserted for the 
sake of comparison (see Plate VII). 
It is a noteworthy fact that, of the seventeen species of 
fresh-water Amphipoda known to occur in North America, ten 
are inhabitants of underground waters. Some of these occur 
in caves, such as Gammarus purpurascens and Niphargus am 
