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
It is not possible to count the exact number of limbs, but one gets
the impression that on the left side of this specimen there are
twenty-one sets of appendages, six of which of course belong to the
thorax. On the thorax and anterior part of the pygidium, successive
endopodites show the propodites and dactylopodites becoming
progressively more slender and shorter, while the ischiopodites,
meropodites and carpopodites become shorter and more triangular, and
with increasingly large numbers of short spines on their posterior
borders. Back of the fourth endopodite on the pygidium it is not
possible to make out the detail, but the appearance is of an
endopodite consisting of short broad segments fringed at the back with
short spines, the ones at the very posterior end appearing to be
exceedingly short and rudimentary.
The exopodites are not so well shown as in some others but the setæ
are flattened and blade-shaped, and often bear numerous small spines.
_Measurements:_ Length (lacking most of the fringe), 10.5 mm. Width of
thorax, 10.5 mm. Length of hypostome, 1.41 mm., width at front, 1.46
mm. The distance from back of fringe to end of antennules is 5.4 mm.
If straightened out, the left antennule would be about 6.1 mm. long.
In the first 3.1 mm., there are only ten segments, so that the average
length of a segment is 0.31 mm. The distance from the inner end of the
endobase of the first segment of the thorax to the outer end of the
meropodite is 2.43 mm., and from that point to the end of the
dactylopodite 2.47 mm. making the total length 4.90 mm. These
measurements are taken from the photograph. Measurements taken from
Professor Beecher's drawing, which was made with the camera-lucida,
give a total length of 4.57 mm., the distance to the outer end of the
meropodite being 2.3 mm. and thence to the tip of the dactylopodite
2.27 mm. Detailed measurements of the segments, on the photograph, are
as follows: coxopodite, 0.321 mm.; basipodite, 0.78 mm.; ischiopodite,
0.68 mm.; meropodite, 0.642 mm.; carpopodite, 0.642 mm.; propodite,
1.01 mm., dactylopodite, 0.825 mm.
Specimen No. 235 (pl. 7, fig. 2; pl. 8, fig. 3; pl. 9, figs. 1, 2).
Illustrated: Amer. Jour. Sci., vol. 49, 1895, pl. 3, figs. 5, 6.
Specimens 235 and 236 were originally parts of an entire
_Cryptolithus_, but, as Professor Beecher has explained, the specimen
was cut in two longitudinally on the median line, and the halves
transversely just back of the cephalon, so that each now represents
one half of a thorax and pygidium. Both halves have been cleaned from
both upper and lower side, a perfectly marvelous piece of work, for
the thickness is no greater than that of a thin sheet of paper, and
the soft shale of the matrix has a very slight cohesive power.
Public-domain text, read in full here on John Shaqi.
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