Figs. 4 and 5. Endopodites, probably from a species of _Calymene_. 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 photograph are poor, but show that in this genus the endopodites are like those of Triarthrus. × 8.5. Fig. 7. _Cryptolithus tessellatus_ Green. Specimen 234. This specimen shows well the backward directed antennules and also the outer segments of some of the cephalic endopodites. × 11. PLATE VI. HELIOTYPE CO. BOSTON * * * * * PLATE 7. Photographs of _Cryptolithus tessellatus_ Green, made by C. E. Beecher. Fig. 1. Specimen 233. The best preserved individual, the one from which Professor Beecher's drawing (text fig. 45) was made, and which served as the principal basis for the restoration (text fig. 20). Note the long, backward directed antennules, the abrupt backward turn of the outer portions of the endopodites, the way in which the exopodites extend beyond the endopodites, and the fact that alt are beneath the cover of the dorsal shield. The hypostoma is turned entirely around. × 10.9. Fig. 2. Specimen 235. Half of the thorax and pygidium, with the appendages revealed from the ventral side. Note the abrupt manner in which the outer portions of the endopodites are turned backward. See also pl. 8, fig. 3, and pl. 9, fig. 1 (right half). × 14.45. Fig. 3. Specimen 236. Detail from fig. 4, to show the blade-like setæ of the exopodites and the numerous terminal spines of the endopodites. × 30. Fig. 4. Specimen 236. The appendages of the thorax and pygidium, seen from the lower side. Specimen 236 is the right half of the same individual from which specimen 235 was obtained. Note the interarticular membranes between the segments of the endopodites and the blade-like setæ of the exopodites. See also pl. 9, fig. 1 (left side). × 19. Fig. 5. Specimen 236. The same specimen, seen from the dorsal side, showing, when the test is removed, the long blade-like setæ of the exopodites. See also pl. 9, fig. 2 (right half). × 19. PLATE VII. HELIOTYPE CO. BOSTON * * * * * PLATE 8. Photographs of _Cryptolithus tessellatus_ Green, made by C. E. Beecher. Fig. 1. Specimen 231. A nearly complete individual, cleaned from the ventral side and showing obscurely the hypostoma and fragments of numerous appendages. Note the lines of appendifers along the sides of the axial lobe. × 11. Fig. 2. Specimen 232. Although this is not very well preserved, it shows more of the cephalic appendages than any other. Even so, only just enough is shown to indicate that they were similar to those on the thorax. × 12.