l6o THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. 
The exopodites and endopodites of the left side of the thorax are best preserved. The 
exopodites are above the endopodites, and only that portion exposed from the ventral side 
which projects beyond the line at which the endopodites bend backward. The endopodite 
on the left side of the first thoracic segment is the best preserved. It shows seven segments, 
the outer ones best. The coxopodite is short and narrow, the basipodite somewhat heavier 
and longer, while the carpopodite and propodite are the widest and strongest segments. The 
propodite is triangular and flattened, like the segments on the middle and posterior part of 
the thorax of Triarthrus. At the inner end of the ischiopodite and meropodite are tufts of 
spines pointing inward and backward. These are not shown on any of the photographs, 
but may be seen with the light striking the specimen at the proper angle. 
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 tri- 
angular, 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 rudi- 
mentary. 
The exopodites are not so well shown as in some others but the setse 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 
Avould 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 endo- 
base 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 (pi. 7, fig. 2; pi. 8, fig. 3; pi. 9, figs. 1, 2). 
Illustrated : Amer. Jour. Sci., vol. 49, 1895, pi. 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. 
Both sides of specimen 235 were figured, but the dorsal side was apparently then some- 
