306 Percoidea, or Perch-like Fishes 
gate in body, with the vertebre in increased number and with 
only two spines in the anal fin. About ninety species are 
recorded, the vast majority being American. The dwarf perches, 
called darters (Etheostomine), are especially characteristic of 
the clear streams to the eastward of the plains of the Missouri. 
These constitute one of the greatest attractions of our American 
river fauna. They differ from the perch and its European allies in 
their small size, bright colors, and large fins, and more technic- 
ally in the rudimentary condition of the pseudobranchie and 
the air-bladder, both of which organs are almost inappreciable. 
The preopercle is unarmed, and the number of the branchioste- 
gals is six. The anal papilla is likewise developed, as in the 
Gobiide, to which group the darters bear a considerable super- 
ficial resemblance, which, however, indicates no real affinity. 
Relations of Darters to Perches. —The colors of the Ethe- 
ostomine, or darters, are usually very brilliant, species of 
Etheostoma especially being among the most brilliantly colored 
fishes known; the sexual differences are often great, the females 
being, as a rule, dull in color and more speckled or barred than 
the males. Most of them prefer clear running water, where 
they lie on the bottom concealed under stones, darting, when 
frightened or hungry, with great velocity for a short distance, 
by a powerful movement of the fan-shaped pectorals, then 
stopping as suddenly. They rarely use the caudal fin in swim- 
ming, and they are seldom seen floating or moving freely in 
the water like most fishes. When at rest they support them- 
selves on their expanded ventrals and anal fin. All of them 
can turn the head from side to side, and they frequently lie 
with the head in a curved position or partly on one side of the 
body. The species of Ammocrypta, and perhaps some of the 
others, prefer a sandy bottom, where, by a sudden plunge, 
the fish buries itself in the sand, and remains quiescent for 
hours at a time with only its eyes and snout visible. The 
others lurk in stony places, under rocks and weeds. Although 
more than usually tenacious of vitality, the darters, from their 
bottom life, are the first to be disturbed by impurities in the 
water. All the darters are carnivorous, feeding chiefly on the 
larvee of Diptera, and in their way voracious. All are of small 
size; the largest (Percina rex) reaches a length of ten inches, 
