PART IV. 
DESCRIPTION OF THE APPENDAGES OF INDIVIDUAL SPECIMENS. 
Triarthrus becki Green. 
In order to make easily available the evidence on which the present knowledge of the 
appendages of Triarthrus and Cryptolithus rests, it has seemed wise to publish brief descrip- 
tions and photographic figures of some of the better specimens preserved in the Yale Uni- 
versity Museum. These specimens are pyritic replacements, and while they do not as yet 
show any signs of decomposition, it should be realized that it is only a matter of time when 
either they will be self -destroyed through oxidation, or else embedded for safe keeping in 
such a fashion that they will not be readily available for study. It is therefore essential to 
keep a photographic record of the more important individuals. 
Specimen No. 220 (pi. 3, fig. 2). 
Illustrated: Amer. Geol., vol. 15, 1895, pi. 4 (drawing); Amer. Jour. Sci., vol. 13, 1902, pi. 3 
(photograph). 
This is one of the largest specimens showing appendages, and is developed from the ven- 
tral side. It shows some appendages on all parts of the body, but its special features are 
the exhibition of the shafts on the proximal ends of the antennules, the rather well pre- 
served appendages of the cephalon and anterior part of the thorax, and the preservation of 
the anal opening. In the drawing in the American Geologist, the right and left sides are 
reversed as in a mirror, a point which should be borne in mind when comparing that figure 
with a photograph or description. 
The shaft of the left antennule is best preserved and is short, cylindrical, somewhat 
enlarged and ball-shaped at the proximal end. It is 1.5 mm. long. The posterior part of 
the hypostoma is present, but crushed, and the metastoma is not visible, the pieces so indi- 
cated in Beecher's figure being the rim of the hypostoma. Back of the hypostoma may be 
seen four (not three as in Beecher's figure) pairs of gnathites, the first three pairs broad 
and greatly overlapping, the fourth pair more slender, but poorly preserved. The inner 
edges of the gnathites on the right side are distinctly nodulose, and roughened for mastication. 
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 cylin- 
drical, 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 setae 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 exopo- 
dite there is a minute spine at each joint. 
Measurements: Length, 38 mm.; width at back of cephalon, 19 mm. 
Specimen No. 210 (pi. 2, fig. 3). 
Illustrated: Amer. Jour. Sci., vol. 46, 1893, p. 469, fig. 1 (head and right side); Amer. Geol., vol. 13, 
1894, pi. 3, fig. 7 (same figure as the last) ; Amer. Jour. Sci., vol. 13, 1902, pi. 2, fig. I (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 
