JELLY-FISHES. 



107 



stem is developccl, aiul the neetostem has little in common with that of Ajdlma. The 

 ncc-tocalices are of characteristic shape and different from those of any other siphono- 

 ])hore. Each bell has the shape of a horse's hoof, 

 and has a very shallow cavity and rigid walls. As 

 far as yet known the lIi])i>opodia! have no diphyi- 

 zooids snch as exist in several genera of the Dijiliyie. 



OiiDKU IV. — DISCOIDE.E. 



Among the many interesting forms of Medusie 

 related to, and by most naturalists included in the 

 Sijihonophora, are two beautiful genera called ^'cMla 

 and Porpita. These, with a genus Matafla, which is probably the joung of one or 

 the other, make up a group called the Discoideai. 



Velella has borne the name which designates its most strikino- peculiaritv since the 

 middle of the fifteenth century, on account, perhaps, of a somewhat fanciful likeness 

 to a little sail. It is commonly called in Florida, where it is sometimes very abundant, 

 the "float," and is likewise commonly confounded with the P%.s«//(r or Portuguese 

 man-of-war. The body or disk of Velella has an oblong sliajie, flattened u]ion its 



Fig. lul.— lijpLj 



Upper and lower sides. The float is composed of a number of Cdncentrie comjiart- 

 nients in free communication with each otlier, seven of which o]ien externally in a line 

 extending diametrically across the disk. In the whole diametei- there are fcmrtcen 

 such openings, seven in each radius. 



A triangular sail rises on the ujjper side of the Velella disk and extends diagonally 

 across its surface. It is firmly joined to the upper plate of the float. Over the trian- 

 gular sail as well as the float, there is stretched a thin, blue-colored membrane, which is 

 <c>ntinued into a variegated soft rim along its border and around the rim of the float. 

 In our most common American Velella, which often reaches a length of four or five 

 inches, the portion of the rim of this membrane around the disk is entire; in some 

 species, however, it is continued into elongated a])i)endages. 



The most imjwrtant appendages are found on the under side of the Velella disk 



