[Illustration: Fig. 4. _Neolenus serratus_ (Rominger). One of the so-called epipodites of specimen 65515, showing that it has the same outline as an exopodite (compare figure 3) and fragments of setæ on the margin. × 3.] The anterior edge of the shaft shows a narrow stiffening ridge and the setæ are but little longer than its greatest width. The second segment of the pygidium has another exopodite like this one, but shows faintly the line between the two lobes, as though there were two segments. This specimen also shows some very well preserved endopodites, but they differ in no way from those described from specimen No. 58589. Walcott mentions two large epipodites projecting from beneath the exopodites. I judge that he has reference to the distal lobes of the exopodites, but as these are continuous with the main shaft, there can be no other interpretation of them than that which I have given above. _Measurements:_ The pygidium is 19 mm. long (without the spines) and about 34 mm. wide at the front. The exopodites show faintly beneath the pygidial shield, but their proximal ends are too indistinct to allow accurate measurement. Apparently they were just about long enough to reach to the margin of the shield. The best preserved one, that of the second segment in the pygidium, is about 11 mm. long, 2.5 mm. wide at the widest; the distal lobe is 2.5 mm. long, and the longest setæ of the main lobe 3.5 mm. long. The pleural lobe of the pygidium is just 11 mm. wide at this point. The endopodites project from 8 to 12 mm. beyond the pygidium, showing about four segments. The thoracic exopodite described above is 11 mm. long and 2.75 mm. wide at the widest part. The distal lobe is 3.5 mm. long and 2.25 mm. wide, and the longest setæ on the main lobe 3 mm. long. Specimen No. 65519. Illustrated: Walcott, Zittel-Eastman Text-book of Paleontology, vol. 1, 1913, fig. 1343;--Smithson. Misc. Coll., vol. 67, 1918, pl. 21, fig. 6. This specimen is somewhat difficult to study but is very valuable as showing the natural position of the exopodites of the anterior part of the thorax. Walcott's figures are excellent and show the broad leaf-like shafts, the distal lobes with the re-entrant angles in the posterior margin, and the long fine setæ of the main lobes. None of the distal lobes retains its setæ. All extend back to the dorsal furrows, but the proximal ends are not actually shown. The specimen is especially important because it shows the same distal lobes as specimen No. 65514, and demonstrates that they are a part of the exopodite and not of any other structure. _Measurements:_ The exopodite belonging to the fourth thoracic segment is 23 mm. long and 4 mm. wide at the widest part. The longest setæ are 7 mm. in length. Specimen No. 65520. Illustrated: Walcott, Smithson. Misc. Coll., vol. 67, 1918, pl. 20, fig. 2; pl. 22, fig. 1.