CAVE FISHES OF NORTH AMERICA. 385 
Doctor Kigenmann has worked out the following key to the Ambly- 
opsidee, based on the structure of the eye: 4 
a. Vitreous body and lens normal, the eye functional; no scleral cartilages; eye per- 
manenily connected with the brain by the optic nerve; eye muscles 
normal; no optic fiber layer; minimum diameter of the eye 
(0D) ERA re es Meee ee meee er nee ae Tha ce ee te Chologaster. 
b. Eye in adult more than 1 mm. in longitudina! diameter; lens over 0.5 mm. in 
diameter; retina very simple, its maximum thickness 83.5 « in the 
old; the outer and inner nuclear layers consisting of a single series 
of cells each; the ganglion layer of isolated cells; maximum thick- 
ness of the outer nuclear layer 5 y, the inner layer 8 je... -cornutus. 
bb. Eye in adult less than 1 mm. in longitudinal diameter; lens less than 0.4 mm.; 
outer nuclear layer composed of at least two layers of cells; the 
inner nuclear layer of at least three layers of cells, the former at least 
10 uw thick, the latter at least 18 x. 
c. Pigment epithelium 65 mm. thick in the middle aged, 102 in the 
CNG Neil Se = Bake ae Ss Ga eee cee tae 5 aera ee aa Neem OR me papuliferus. 
ec. Pigment 49 4 thick in the middle aged, 74 in the old; 24 to 30 per cent 
thinner than in papilliferus; eye smaller.................- agassizit. 
aa. The eye a vestige, not functional; vitreous body and lens mere vestiges; the 
eye collapsed, the inner faces of the retina in contact; maximum 
diameter of the eye about 200 y. 
d. No scleral cartilages; no pigment in the pigment epithelium; a minute 
vitreal cavity; hyaloid membrane with blood vessels; pupil not 
closed; outer nuclear, outer reticular, inner nuclear, inner reticular, 
ganglionic, and pigment epithelium layers differentiated; cones 
probably none; no eye muscles; maximum diameter of the eye 
180° 4; eye probably connected with the brain throughout 
TORSO eo Neg re ae eg em a a eed ee ON Typhlichthys. 
dd, Scleral cartilages present; pigment in the pigment epithelium; vitreal 
cavity obliterated; no hyaloid membrane; pupil closed; some of 
the eye muscles developed; no outer reticular layer; inner and 
outer nuclear layers merged into one; eye in the adult not cennected 
with the brain. 
e. Pigment epithelium well developed; cones well developed; gang]lonic 
cells forming a funnel-shaped mass through the center of the eye; 
pigment epithelium over the front of the eye without pigment; 
maximum diameter of the eye about 200 w_......-2222 22 Amblyopsis. 
ee. Pigment epithelium developed on the distal face of the eye, rarely 
over the sides and back; no cones; nuclear layer mere vestiges; the 
ganglionic layers restricted to the anterior face of the eye just 
within the pigment epithelium; maximum diameter of the eye 
DEOL oe) leere ee rset eres See es te ee a ak 8 Troglichthys. 
CHOLOGASTHR Agassiz. 
Cholegaster Agassiz, Amer. Jour. Sci. and Arts, XVI, 1853, 135 (cornutus). 
The genus Chologaster is distinguished from the other genera of the 
Amblyopside by the presence of well-developed eyes, which vary 
greatly in the different species of the genus. All of the species pos- 
«Kigenmann, Eyes of the Blind Vertebrates of North America, Archiv ftir 
Entwickelungsmechanik der Organismen, VIII, 1899, 607. 
F. C. 1904—25 
