The pedalia conform entirely to the description given those of Charybdea, except that there are three attached to the bell margin in each interradius instead of one, and that the blade of each pedalium is much narrower.
The sensory clubs also show exactly the same relation to the bell and exactly the same structure.
In the bell cavity the proboscis has a longer and better defined stalk than that of Charybdea, and has the further and more important difference of possessing special sensory organs, to the number of fifteen or twenty. The suspensoria are much more developed than in Charybdea, so that the interradial funnels lying between are more marked. In a corresponding way the frenula are larger and stouter (Figs. 28, 29, _frn_). The musculature shows no new features and differs only in being comparatively more strongly developed and having a more pronounced striation. The nerve ring follows the same looped course from the margin in each interradius up to the level of the sensory clubs in the perradius.
The stomach offers no peculiarities, and the phacelli also agree with those of Charybdea except in having a smaller number of filaments in each tuft. The stomach pockets are not guarded by such well-developed valves as those described for Charybdea, though the valvular nature of the lips of the gastric ostia is indicated and the valvular functions undoubtedly performed. The gastric ostia are smaller (cf. Figs. 7 and 22), and this makes highly developed valves less necessary. No trace of anything corresponding to mesogonial pockets was noticed.
In the matter of the marginal pockets, however, we find that the agreement with Charybdea is no longer continued. The regions that correspond to the eight marginal pockets of Charybdea are formed, as in that genus, by the coming together of the exumbrella and subumbrella at the sensory niche (Figs. 25-28), but each of these regions is subdivided, as it is not in Charybdea, into two marginal pockets, a larger (_mp_, Figs. 28-29) and a smaller (_mp´_). In this way sixteen marginal pockets are formed as in the Chirodropidæ. Furthermore, as happens in the latter family but does not in the Charybdeidæ, the marginal pockets extend into the velarium. From each of the larger marginal pockets are given off two velar canals, while each of the smaller gives rise to but one short one (Fig. 18). Fig. 30 represents one of the last sections of a Tripedalia cut transversely, in which nothing but the pedalia and the velarium appear, and in it are shown the velar canals (_vc_), which come from the larger marginal pockets. The velarium appears in four segments because it is drawn upwards in the four perradii by the frenula (see Fig. 20). That the canals from the smaller pockets do not appear in the section is due to their shortness and to the fact that they are pulled upwards above the level of the sections by the frenula, together with that portion of the velarium.