62 IOWA STUDIES IN NATURAL HISTORY 
roots. The operculum covers the gills completely and extends 
well back of them, doubtless aiding in retaining water in the gills 
when this peculiar fish is out of its native element. The head, 
with its very large protuberant eyes, resembles that of a grass- 
hopper when viewed in a profile. The two dorsals and the caudal 
fins are finely barred with red, brown and white, while the paired 
fins have little or no markings. The mouth is wide and the out- 
line of the upper lip is broken by two prominent lobe-like descend- 
ing flaps on either side of the middle, giving a most comical ex- 
pression to its physiognomy. The inner surface of the operculum, 
which is all in one piece, is covered by a rather thick membrane 
resembling rubber and reminding one of the lining of the bran- 
chial chamber of some of the land crabs of the West Indies.” 
There is a considerable air space below the gills, between them 
and the bottom of the head, and below the pharyngeal cavity, 
which communicates with the exterior by a slit-like aperture, the 
gill opening; this slit can be closed completely by the operculum. 
There are four gill arches on each side, each armed by two op- 
posite rows of short gill rakers. The gill filaments are stiff, finger- 
like projections shorter, proportionally, than in most fishes, a 
double row supported by each gill arch. There are strong muscles 
so placed as to allow the vertical movement of the whole of the 
gills. Each gill filament is divided transversely with various 
flattened disc-like gill lamelle looking like a pile of lozenges. The 
structure is much like that of the gills found in the chitons. So 
long as these gills keep moist they can perform their function and 
are, I suppose, capable of utilizing the air either in or above the 
water. The whole contrivance suggests that a considerable amount 
of water is kept in the bottom of the large space below the gills 
proper which is so conspicuous a feature. The rest of the gill 
cavity might contain air when the creature was out of water. 
Now the musculature seems adapted to lower the whole pharyn- 
geal apparatus so as to dip the gills into the water from time to 
time and then lift them again into the air which fills the upper 
part of the chamber and which can be renewed as often as neces- 
sary through the mouth. Thus the moistened gills can take care 
of the air by the ordinary process of respiration, as all of the 
necessary elements are present—the thin walls of the gill lamelle 
2See Bahama Expedition p. 97 and Barbados-Antigua Expedition p. 183 
for a discussion of the adaptations for breathing found in the land crabs of 
the West Indian region. 
