PLATE 6. 
All figures except 4 and 5, from photographs by C. E. Beecher. 
Fig. 1. — Triarthrus becki. Specimen 203. A well preserved small individual, showing 
the appendages of the right side of the thorax, x 11.46. 
Fig. 2. — Triarthrus becki. Specimen 209. A well preserved individual, showing the 
antennules and some appendages of thorax and pygidium. For detail of the pygidium, see 
pi. 5, fig. 1. X4. 
Fig. 3. — Triarthrus becki. Specimen 218. Ventral side of the pygidium and greater 
part of the thorax of an individual of medium size. Note especially the relation of exopo- 
dites to endopodites of the last two thoracic segments. A drawing of these appendages is 
shown on text fig. 43. x 4.3. 
Figs. 4 and 5. — Endopodites, probably from a species of Calymcnc. These specimens, 
with several others, are on a small slab of limestone from the Point Pleasant (Trenton) beds 
opposite Cincinnati, Ohio. Specimen in the U. S. National Museum. Photographs by R. S. 
Bassler. 
Fig. 6. — Acidaspis trentonensis Walcott. Both the specimen, No. 245, and the photo- 
graph are poor, but show that in this genus the endopodites are like those of Triarthrus. 
x 8.5. 
Fig. 7. — Cryptoliihus tesscllatus Green. Specimen 234. This specimen shows well the 
backward directed antennules and also the outer segments of some of the cephalic endopo- 
dites. XII. 
