The Appendages, Anatomy, and Relationships of TrilobitesRaymond, Percy E. (Percy Edward)
Science
The Appendages, Anatomy, and Relationships of Trilobites
Raymond, Percy E. (Percy Edward)
Trilobites
The outer ends of one endopodite and three exopodites project beyond
the margin on the right side. The dactylopodite of the endopodite is
especially well preserved. It is cylindrical, the end rounded but not
enlarged or pointed, and bears three small sharp spines, all in a
horizontal plane, one anterior, one central, and one posterior. The
outer ends of the exopodites show about ten segments each (in 2.5 mm.)
beyond the margin of the test, and from three to five setæ attached to
the posterior side of each segment. These hairs are attached in a
groove, well shown in this specimen. On the anterior margin of the
exopodite there is a minute spine at each joint.
_Measurements:_ Length, 38 mm.; width at back of cephalon, 19 mm.
Specimen No. 210 (pl. 2, fig. 3).
Illustrated: Amer. Jour. Sci., vol. 46, 1893, p. 469, fig. 1
(head and right side); Amer. Geol., vol. 13, 1894, pl. 3, fig. 7
(same figure as the last); Amer. Jour. Sci., vol. 13, 1902, pl. 2,
fig. 1 (photograph).
This individual supplied the main basis for Professor Beecher's first
figure showing the appendages of the thorax, the head and appendages
of the right side having been taken from it, and the appendages of
the left side from No. 206. Such of the endopodites as are well
preserved show from three to four segments projecting beyond the test,
and the dactylopodites have one or two terminal spines. The antennules
are unusually well preserved and have about forty segments each in
front of the cephalon, or an average of five to one millimeter.
Specimens 209 and 210 are on a slab about 7 × 5.5 inches, and with
them are twelve other more or less well preserved individuals, all but
one of which are smaller than these. Two of the fourteen are ventral
side up on the slab, which means dorsal side up in the rock. Nine are
oriented in one direction, two at exactly right angles to this, and
three at an angle of 45 with the others. If the majority of the
specimens are considered to be headed northward, then seven are so
oriented, two northeast, one east, two south, one southwest, and one
west.
Nine of the specimens show antennules. Five of these are specimens
headed north, and in all of them the antennules are in or very near
the normal position. The antennules of two, one headed east and the
other west, are imperfectly preserved, but the parts remaining diverge
much more than do the antennules of those in the normal position. The
individual headed southwest has one antennule broken off, while the
other is curved back so that its tip is directed northward. Another
one, headed south, has the antennules in the normal position. These
observations indicate that the specimens were oriented by currents of
water, rather than in life attitudes, and that the distal portions of
the antennules were relatively flexible.
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