Page:Smithsonian Miscellaneous Collections, Volume 85.djvu/120

Rh (b) that they were of a very delicate structure and readily destroyed; (c) that when preserved they were likely to be distorted and displaced by compression in the shale and could only be seen from the ventral side of the flattened carapace when they projected beyond the margin and were outlined on the shale. At first I thought that the eyes were situated on the carapace just within the line of its union with the large antero-lateral spines. Later I re-examined all the specimens showing the eyes, and found two that indicated that the visual surface of the eye was on one side of the suture separating the spines from the carapace, and the cap or palpebral lobe on the other, and one that quite clearly indicated that it was attached to the proximal end of the great spines, the latter being equivalent to the free cheeks of the trilobite. The interpretation of this is that the visual surface of the eye was attached to the great spine outside of the suture that outlined the spine from the carapace, and that the cap or palpebral lobe of the elevated visual surface of the eye was attached to the carapace as in the trilobites with elevated eyes and free cheeks.

It is difficult to determine the extent of the elevation of the eye above the carapace, but from its inconspicuous position in the fossil state I strongly suspect that it was only slightly raised and that its field of vision was largely forward and downward; this would be in accord with the needs of a small, active, free-swimming animal that spent little time on the bottom.

Among the trilobites the eye of Deiphon forbesi Barrande is at the proximal end of a large genal spine forming the free cheek, and the great eye of Bohemilla stupenda Barrande occupies nearly the entire width of the proximal end of the free cheek which is extended into a long strong spine.

Digestive organs.—The intestinal canal extends from the posterior margin of the labrum back to the small, platelike termination of the body; it is contracted a little opposite the line of union of each of the segments (see figs. 6, 7, and 9, pl. 22); anteriorly the intestine widens out between the labrum and carapace to form what may have been the stomach; the narrow canals of the dorsal lobes passed into the space between the carapace and labrum and probably entered the enlarged intestinal canal as did the canals of the antero-lateral spines which appear to pass without interruptions through the close sutures that unite them with the carapace; the canals of the postero-dorsal lobes may represent the shell-glands or excretory organs of the recent Apodidae.