The Semantida (p. 953, Pl. 92) develop a horizontal basal ring at the oral side of the vertical sagittal ring; the basal meshes or lattice gates, which remain between the former and the latter, are the important cortinar pores (one pair jugular, one pair cardinal, p. 954); they usually appear inherited in the cortinar septum of the #Cyrtellaria#. In the Coronida (p. 967, Pls. 82, 94) a second vertical ring (the frontal ring) appears in addition to the sagittal ring; it lies in the frontal plane at right angles to the latter. Finally the Tympanida (p. 987, Pls. 93, 94) have probably arisen from the Semantida by the formation of a second horizontal ring (mitral ring) parallel to the basal and attached to the upper portion of the sagittal ring. 188. _Genealogical Tree of the Spyroidea._--The extensive order #Spyroidea# is of especial interest in connection with the phylogeny of the NASSELLARIA, since all its members show two well-developed skeletal elements in combination, the sagittal ring of the #Stephoidea# and the latticed cephalis of the #Cyrtoidea#; the majority possess also the basal tripod of the #Plectoidea# (or a radial skeleton derived from it). Hence there is a possibility of deriving the stem-forms of the #Spyroidea# from each of these three groups. The four families of this order exhibit similar relationships to those of the four families of #Cyrtoidea#; the common stem-group is the family Zygospyrida; from this the Tholospyrida have arisen by the development of a galea on the apical pole, the Phormospyrida by the addition of a thorax on the basal pole. The Androspyrida may be derived either from the Tholospyrida by the formation of a basal thorax, or from the Phormospyrida by the development of an apical galea. Some groups, however, such as the peculiar Nephrospyrida (Pl. 90) have probably been developed directly from the #Stephoidea#.