148 PALEOZOIC FISHES OF NORTH AMERICA. 
ating bands of the larger cup, which were characters not exhibited by the 
ear stones of any fishes known to me. In these circumstances I was forced 
to regard them as part of the optical apparatus, and a study of the organs 
of sight in fishes of different groups h:s given me the conviction that they 
are the optic capsules, which held the lens and vitreous humor in the broader 
cup—of which the margin perhaps supported a circle of sclerotic plates, 
perhaps was a substitute for them—and that the central perforation was for 
the passage of the optic nerve. In most fishes of the present day the eye 
capsule consists of two hemispherical cartilaginous cups; but in many these 
are bony, and in some, as Ceratodus, Xiphias, ete, they are united to form 
ovoid or cup-shaped bony shells, which hold and support the lens and have 
an orifice for the passage of the optic nerve. 
In many fishes the crystalline lens has a peculiar banded structure, 
and in some—as the cod—the bands radiate from and converge to opposite 
poles, like the meridians on a terrestrial globe, while in others—as salmons 
and sharks—they converge to a line or septum instead of a point at each 
pole. The figure formed by the intersection of the radial fibers and the 
septum is a very elegant one, and precisely that which is found in the bot- 
tom of the hemispherical or semi-elliptical cup of the broader end of the 
conical bones under consideration. In Xiphias and Tetrapterus the eye cap- 
sules are elliptical or sub-globular shells of bone, which inclose all the 
optical apparatus. Over the large orifice the cornea is stretched like a drum- 
head, while below is a smaller opening for the passage of the optic nerve. 
These bony shells are marked at each end of the ellipse by radiating lines much 
like those in the organs which I have considered the eye capsules of Dinichthys, 
and this structure affords additional evidence of homology. 
Taking all these facts into account, I think we may assume with a good 
degree of confidence that in these turbinated bones found in the anterior 
portion of the head of Dinichthys we have the osseous capsules which sup- 
ported the globes of the eye. 
In Owen’s Paleontology, second edition, page 144, it is said that Mr. 
David Page found in the tile-stone of Lanarkshire, Scotland, the base of the 
Devonian system, a Cephalaspis which, with a dorsal, pectoral, and a large 
heterocercal caudal fin, “ had well-marked eye capsules.” 
