This table confirms that made up by Carpenter, and shows even more strikingly the progressive increase in the average number of segments in the trunk throughout the Palæozoic. While the two trilobites with the greatest number of segments are Cambrian, yet on the average, the last of the trilobites had the more numerously segmented bodies. The multisegmented trilobites are: Period Genus Av. No. of Av. No. of Av. No. segments in segments in of trunk thorax pygidium segments ================================================================ Lower Cambrian _Pædeumias_ 44+ 1 45+ Upper Cambrian _Menomonia_ 42 4 46 _Ectenonotus_ 12 22 34 Ordovician _Encrinurus_ 11 22 33 _Dionide_ 6 26 32 Silurian _Harpes_ 29 3 32 Devonian _Coronura_ 11 23 34 _Dalmanites_ 11 23 34 Permian _Anisopyge_ 7+(9?) 30 39? _Anisopyge_, the last of the trilobites, stands third on the list of those having great numbers of segments, and in each period there are a few which have considerably more than the average number. It may be of some significance that of these nine genera only _Pædeumias_ and _Anisopyge_ belong to the Opisthoparia, the great central group, and that five are members of the Proparia, the latest and most specialized order. FORM OF THE SIMPLEST PROTASPIS. It would naturally be expected that the young of the Cambrian trilobites should be more primitive than the young of species from later formations, and Beecher (1895 C) has shown that this is the case. He had reference, however, chiefly to the eyes, free cheeks, and spines, and by comparison of ontogeny and phylogeny, demonstrated the greater simplicity of the protaspis which lacked these organs. It remains to inquire which among the other characteristics are most fundamental.