The Cubomedusæ, as the name implies, approximate cubes, with their tentacles (four in Charybdea) arranged at the four corners of the lower face of the cube. These tentacles are said to lie in the interradii. Half way between any two points of attachment of the pedalia (the basal portions of the tentacles) and a little above the margin of the bell (cube), in a niche, hang the sensory clubs, one on each side, four in all. Each sensory club hangs in a niche of the exumbrella and is attached by a small peduncle whose axial canal is in connection with one of the four stomach-pockets and in the club proper forms an ampulla-like enlargement. Each club is said to lie in a perradius, and, like the tentacles, belongs to the subumbrella. This is shown by the course of the vascular lamellæ, bands of cells that, stretching through the jelly from the endoderm to the ectoderm all around the margin, form the line of division between sub- and exumbrella. Each club has six eyes. Two of these on the middle line of the club facing inwards are called the proximal and distal complex eyes, to distinguish them from the four simple eyes that are disposed laterally, two on each side of the line of the two complex eyes. All of these eyes look inwards into the bell cavity through a thin transparent membrane of the subumbrella. Besides the eyes and the ampulla already mentioned, a concretion fills the lowermost part of the club, and a group of large cells, having a network-like structure and called network cells by Conant, fill the uppermost part of the club between the proximal complex eye and the attachment of the club to its peduncle (Plate II, Fig. 13). What is evidently nerve tissue, fibers and ganglion cells, fills the rest of the club, with two groups of large ganglion cells disposed laterally from the network cells. A sensory (flagellate) epithelium covers the club. Most Cubomedusæ, among them Charybdea, have a velarium (comparable to the velum of the Hydromedusæ), a membrane of tissue that extends inwards at right angles all around the margin. This velarium, like a velum, has a central opening through which the water is expelled from the bell-cavity when the animal pulsates. In the perradii and in the angle between the velarium and the body wall, are the frenula, which give support to the velarium much like brackets support a shelf, except that here the brackets are above the shelf instead of below.