410 ON THE WYANDOTTE CAVE AND ITS FAUNA. 
to feed, and swim in full sight like white aquatic ghosts. They 
are then easily taken by the hand or net, if perfect silence is 
preserved, for they are unconscious of the presence of an enemy 
except through the medium of hearing. This sense is, however, 
evidently very acute, for at any noise they turn suddenly down- 
ward and hide: beneath stones, ete., on the bottom. They must 
take much of their food near the surface, as the life of the depths 
is apparently very sparse. This habit is rendered easy by the 
structure of the fish, for the mouth is directed partly upwards, and 
the head is very flat above, thus allowing the mouth to be at the 
surface. It thus takes food with less difficulty than other surface 
feeders, as the perch, etc., where the mouth is terminal or even 
inferior ; for these require a definite effort to elevate the mouth to 
the object floating on the surface. This could rarely be done 
with accuracy by a fish with defective or atrophied visual or- 
gans.* It is therefore probable that fishes of the type of the 
Cyprinodontide, the nearest allies of the Hypseide, and such 
Hypsæidæ as the eyed Chologaster, would possess in the position 
of the mouth a slight advantage in the struggle for existence. 
The blind crawfish above mentioned is specifically distinct jas 
that of the Mammoth Cave, though nearly related to it. Its opu 
are everywhere less developed, and the abdominal margins ant 
cheles have different forms. I call it Orconectes inermis, separating 
it generically from Cambarus, or the true crawfishes, on account of 
the absence of visual organs. The genus Orconectes, then, is estab- 
lished to include the blind crawfishes of the Mammoth and Wie 
dotte Caves. Dr. Hagen, in his mdnograph of the American 
Astacide, suspects that some will be disposed to separate the 
but thinks 
Vie 
Ty 
characters might be suspected of having been deriv 
by modification, or assumed in descent. The preval 
of the Amblyo? 
explains the A 
= *Mr. Putnam’s objection to my reasoning from the structure 
mouth was based on a misconception of my meaning. The above 
more fully. 
f Origin of Genera, p. 41. 
