1880. ] The Structure of the Eye of Trilobites. 505 
made of the eyes of Trilobites to compare with those of Limu- 
lus, he very generously sent me his own collection of sections of 
the eyes of Asaphus gigas and Bathyurus longistrinosus, which he 
had prepared for his own study, also other eyes, and especially 
the shell or carapace of a large Asaphus, from Trenton Falls, 
showing the eye and the projecting points of the corneal lenses. 
Prof. Samuel Calvin kindly sent me the eyes of an unknown Tri- 
lobite from the Trenton limestone, one specimen showing thẹ pits 
made in the mud by the projecting ends of the corneal lenses, 
while to Mr. Whiteaves I am indebted for a well preserved eye 
of Phacops. To Dr. C. A. White, Palæontologist of the U. S. Geo- 
logical Survey, I am also indebted for eyes of Calymene. 
First turning our attention to the casts and natural sections ; 
that of the interior of the carapace, including the molted cornea 
of Asaphus gigas, is noteworthy. When the concave or interior 
Fic. t.—Section of hard parts of eye of Limulus; c, cornea; in, integument : pes 
pore canals; ¢/, corneal lens. X 30 diams. FIG. Ia, optical section of facets. 
surface of this specimen is placed under a magnifying power of 
fifty diameters, the entire surface is seen to be rough with the 
ends of the minute solid conical corneal lenses which project 
into the body-cavity. This is exactly comparable with the cast 
shell of Limulus and its solid corneal lenses projecting into the 
body cavity (Fig. 1). Those of Asaphus only differ in being 
much smaller and more numerous, and perhaps rather more 
blunt. Without much doubt the ends of the corneal lenses of 
Asaphus, as in Limulus, were enveloped in the retina, the animal 
molting its: carapace, the hypodermis with the retina being 
retained by the trilobite, while the corneal lenses were cast with 
the shell, 
In the specimen of the unknown trilobite from Iowa, received 
from Prof. Calvin, the corneal lenses, seen externally, are quite far 
apart, arranged in quincunx order ; the lenses are round and decid- 
edly convex on the external surface. Ina natural section, where the 
VOL, X1V.—No. Vit. 33 
