Illustrated: Amer. Jour. Sci., vol. 13, 1902, pl. 2, figs. 4, 5 (reproduced from photographs).
This specimen, which is developed from the dorsal surface, shows especially well nine appendages of the left side. The first represent the last segment of the cephalon; the remainder belong to the thorax. As is usual, the exopodites of these appendages overlie and curve behind the endopodites. All the exopodites have lost their setæ and the segments of the endopodites are flattened by crushing. The endopodites, while retaining only one or two of the movable spines, have the cup-like bases of from two to four on each of the visible segments, namely, the meropodite, carpopodite, propodite, and, in one case, the dactylopodite. These appendages, although really marvellous in preservation, are of such small size and react so badly to light that their study is very difficult, and Professor Beecher, who had observed hundreds of specimens through all stages of the laborious process of cleaning the matrix from them, undoubtedly was much better equipped to interpret them than any other person.
The drawing is made on the assumption that the appendages are displaced and all moved uniformly outward so that the distal ends of the coxopodites emerge from under the pleural lobe, whereas these ends would normally be under the dorsal furrow, and the distal end of the ischiopodite should reach the margin of the pleural lobe. While it seems very remarkable that it should happen, that all the appendages should be so moved that they would lie symmetrically a few millimeters from their normal position, nevertheless it is found on measuring that they bear the same proportion to the length and width that the appendages of other specimens do, thus indicating that Professor Beecher's interpretation of them was correct. I am unable, however, to see the coxopodites which he has drawn as articulating with the two branches of the limb.
Fig. 42.—Triarthrus becki Green. Appendages of specimen 204. Inked in by Miss Wood from the original tracing. × 10.
This individual shows, better than any other, the connection of the exopodite with the endopodite. Even though the coxopodites are gone, the two branches of each appendage remain together, showing that the basipodite as well as the coxopodite is involved in the articulation with the exopodite. Just what the connection is can not be observed, but there seems to be a firm union between the upper surface of the basipodite and the lower side of the proximal end of the exopodite, as indicated diagrammatically in text [figure 33].
Measurements: The specimen is 20 mm. long and 9 mm. wide at the back of the cephalon. From the tubercle on the middle of the first segment of the thorax to the tip of the corresponding appendage the distance is 8 mm. The entire length of the exopodite of the first thoracic segment is 4.6 mm. The exopodite of the appendage belonging to the seventh segment is only 3.5 mm. long. The pleural lobe is 2.5 mm. wide at the front of the thorax.
Specimen No. 205 ([pl. 2, fig. 4]).
Illustrated: Amer. Jour. Sci., vol. 13, 1902, pl. 5, figs. 2, 3 (photographs).