The endopodites of _Ceraurus_, _Calymene_, and _Isotelus_ are all relatively slender, the segments are parallel-sided, and there seems to be no particular modification from front to back of the thorax. The endopodites of _Isotelus_ are short, the entire six segments of one being but little longer than the coxopodite of the same appendage. The segments of the endopodites of _Neolenus_ are mostly short and wide, and at the distal end of the terminal segment there are three stout spines. In _Kootenia_ the endopodites are long and very slender. The endopodites of Ptychoparia are too poorly preserved to show details, and those of the thorax of _Acidaspis_ likewise reveal little structure, but they seem to have the triangular modification, and to turn back somewhat sharply at about the position of the carpopodite. _Pygidium._ Beecher showed that in _Triarthrus_ there was a pair of appendages on the pygidium for every segment of which it is composed except the last or anal segment (protopygidium). Walcott has since shown that in _Neolenus_ this segment bears a pair of cerci, and Beecher's drawings show that in his later studies he recognized a spinous plate, the possible bearer of cerci, on the anal segment of _Triarthrus_. The appendages of the anal segment have not yet been seen on other species of trilobites. The appendages of the pygidium do not show any special modifications, but seem in all cases to be similar to those of the posterior part of the thorax. In _Cryptolithus_ all the pygidial appendages are short and remain beneath the cover of the dorsal test, while in _Triarthrus_ and _Neolenus_ they extend behind it. In the latter genus the endopodites of the pygidial appendages appear to be practically identical in form with those of the thorax, the individual segments being perhaps a little more nearly square in outline. Like those of the thorax, the segments of the pygidial endopodites bear numerous short spines. The caudal cerci are richly segmented, slightly flexible, spinous tactile organs. They are symmetrically placed, nearly straight when in their natural position, and make an angle of about 75 with one another. They appear to be attached to a narrow rim-like plate which seems to fit in just ahead of the doublure of the pygidium, or perhaps over it. In _Ceraurus_, _Calymene_, and _Isotelus_, the endopodites of the pygidium are similar to those of the thorax, but seemingly more slender, with less well developed coxopodites, and with, in the last-named genus, slender cylindrical segments. Exopodites are not known on the pygidia of any of these genera, but since they are present and like those of the thorax in _Triarthrus_, _Cryptolithus_, _Neolenus_, and _Ptychoparia_, there is little reason to think that they were absent in _Ceraurus_ or _Calymene_, though there is some question about _Isotelus_.