(d) _The Velarium._ Charybdea, like most of the Cubomedusæ, possesses a velum-like structure around the opening of the bell cavity (Fig. 3, _v_). The velarium is a thin muscular diaphragm, resembling the true velum in position and essential structures, but differing from the velum in its origin, and in the possession of diverticula from the gastro-vascular system, the velar canals. Of these there are in C. Xaymacana very regularly sixteen, four in each quadrant. Their outline is seen in Fig. 3 to be forked with small irregular accessory processes. As for its origin, the velarium of the Cubomedusæ is commonly accounted to have arisen by fusion of marginal lobes, as in the case of the velarium of the Discomedusæ. Pending decisive ontological evidence, the slight notches in the four perradii seen in Fig. 3 may perhaps be taken as slight indications of a primitive unfused condition, but the question will be brought up again when the vascular lamellæ are discussed. (e) _The Frenula._ Just as the stomach is attached to the walls of the subumbrella in the four perradii by the suspensoria, so in the lower part of the bell cavity the velarium is attached to the wall of the subumbrella in the perradii by four structures similar to the suspensoria, the frenula velarii. The frenula, like the suspensoria, resemble the brackets of a shelf, with the difference that in the case of the frenula the bracket is above the shelf, their purpose being evidently to keep the velarium stiff against the outflow of water produced by the pulsations of the bell. According to the greater need of strength in this case, we find the frenula stouter, more buttress-like than the suspensoria. The gelatinous ridge that gives them the necessary firmness is thickened so as to be triangular in section, as shown in Fig. 16 (_frn_). (f) _Musculature._ As is general in medusæ, the muscular system, so far as known, is restricted to the subumbrella. It has a very simple arrangement, consisting of a continuous sheet of circular (_i. e._ horizontal) striated fibres, which is interrupted only in the four perradii by the radially directed muscle fibres of the suspensoria and the frenula. In each quadrant, between the muscle of the suspensorium above and that of the frenulum below, in an area just internal to the sensory niche, there lies a space free from muscle. This interruption of the muscle layer is shown in Fig. 39. Under the head of musculature belonging to the subumbrella must be included also the radial, or longitudinal muscles at the bases of the pedalia, which were mentioned before (Fig. 16, _mt_). The mouth lobes and proboscis also are highly contractile and muscular.