The average of thoracic segments for the entire thirty-three genera is 10.5, of pygidial segments 5.9, a total average of 16.4. It will be noted that the thorax shows on the average less and the pygidium more segments than in the Lower Cambrian. If the Agnostidæ could be included, this result would doubtless be still more striking. Of the genera considered, _Asaphiscus_ with 7-11 thoracic and 5-8 pygidial segments, _Blainia_ with 9 thoracic and 6-11 pygidial, _Zacanthoides_ with 9 thoracic and 5 pygidial, and _Anomocare_ with 11 thoracic and 7-8 pygidial segments came nearest to the average. Only a few departed widely from it. The genera tabulated were _Acrocephalites_, _Alokistocare_, _Crepicephalus_, _Karlia_, _Hamburgia_, _Corynexochus_, _Bathyuriscus_, Poliella, _Agraulos_, _Dolichometopus_, _Ogygopsis_, _Orria_, _Asaphiscus_, _Neolenus_, _Burlingia_, _Blainia_, _Blountia_, _Marjumia_, _Pagetia_, _Eodiscus_, _Goniodiscus_, _Albertella_, _Oryctocara_, _Zacanthoides_, _Anomocare_, _Anomocarella_, _Coosia_, _Conocoryphe_, _Ctenocephalus_, _Paradoxides_, _Ptychoparia_, _Sao_, and _Ellipsocephalus_. Enough genera of Upper Cambrian trilobites are not known from entire specimens to furnish satisfactory data. Excluding from the list the Proparia recently described by Walcott, the average total trunk segments in ten genera is 18, but as most of the genera are Olenidæ or olenid-like, not much weight can be attached to these figures. For the Cambrian as a whole, the average for sixty-two genera is between 17 and 18 trunk segments, which is surprisingly like the result obtained by Carpenter from only twelve genera, and tends to indicate that it must be somewhere near the real average. If the 5 or 6 segments of the head be added, it appears that the "average" number of segments is very close to the malacostracan number 21. Genera with 16 to 18 trunk segments are Callavia, _Protypus_, _Bathynotus_, _Crepicephalus_, _Bathyuriscus_, _Ogygopsis_, _Burlingia_, _Orria_, _Asaphiscus_, _Blainia_, _Zacanthoides_, _Neolenus_, _Anomocare_, _Conocoryphe_, _Saukia_, _Olenus_, and _Eurycare_. The order Proparia originated in the Cambrian, and Walcott has described four genera, one from the Middle, and three from the Upper. The number of segments in these genera is of interest. _Burlingia_, the oldest, has 14 segments in the thorax and 1 in the pygidium. Of the three genera in the Upper Cambrian, _Norwoodia_ has 8-9 segments in the thorax and 3-4 in the pygidium; _Millardia_ 23 in thorax and 3-4 in pygidium; and _Menomonia_ 42 in thorax and 3-4 in pygidium. It is of considerable interest and importance to note that the very elongate ones are not from the Middle but from the Upper Cambrian.