The endopodites of most of the appendages of the thorax are well shown, and occasional portions of exopodites. The coxopodites are long, flattened, and do not taper much. The anterior and posterior edges of the basipodites of the endopodites of the first two segments are approximately parallel, but on the succeeding endopodites the basipodites and ischiopodites are triangular in form, with the apex backward. In successive endopodites toward the posterior end, the angle made by the backward-directed sides of the basipodites becomes increasingly acute, so that in some of the posterior appendages this segment is wider than long. The ischiopodite shows a similar increase of width and angularity on successive segments, and the meropodites and carpopodites also become wider on the posterior segments, and even triangular in outline toward the back of the thorax and on the pygidium.
Along the median portion of the axial lobe the specimen has been cleaned until the inner side of the ventral membrane was reached. Here the test shows on the inner surface at each segment of the thorax a series of low ridges which are roughly parallel to the axial line, but which really converge in an anterior direction. Between the ridges are shallow canoe-shaped depressions, which have the appearance of areas for the insertion of muscles.
Measurements: Length, 31 mm.; width at back of head, 15 mm.; distance, in a straight line, from point of insertion of the right antennule to its tip, 14.25 mm.; it projects 12 mm. beyond the cephalon.
Fig. 43.—Triarthrus becki Green. Drawing to represent the writer's interpretation of the appendages of specimen 218. Drawn by Miss Wood. × 10.
Specimen No. 218 ([pl. 6, fig. 3]; text [fig. 43]).
This specimen is a large one, developed from the lower side, but retains only the endopodites of a few appendages. The cephalon and anterior portion of the thorax are missing.
Professor Beecher had a drawing made to show the appendages on the right-hand side of the last two segments of the thorax, seen of course from the ventral side. This drawing shows well the broadening of the basipodite, ischiopodite, and meropodite, while the coxopodite is thick and heavy, and the inner end of the gnathobase somewhat rugose. Almost every segment of the endopodites has one or more pits for insertion of spines, these being along the anterior or posterior margins. The exopodites lack the setæ, but show no unusual features.
Specimen No. 222 ([pl. 4, fig. 5]).