REPORT ON THE DEEP-SEA MEDUSAE. 91 



extension and strength of the fulcra] capsule increases proportionately with that of the 

 ovum enclosed. The ripest ovum of Periphema regina reaches the extraordinary size 

 of a millimeter and more. The ova consist for the most part of an opaque food yolk, 

 composed of spheroidal yolk granules of equal size (O'Ol mm. diameter), thickly com- 

 pacted (fig. 4, yd). Each ripe ovum is also enclosed (inside the fulcral sheath) by a 

 thick structureless (?) chorion (fig. 4, yc), showing a projecting micropyle at one spot 

 (fig. 4, ym). It has the form of a short bottle neck, and resembles the micropyle known 

 in the eggs of our freshwater mussels (Naiadacea). Below the micropyle we can 

 distinguish with the naked eye a white spot (" cicatricula ") on the yellow yolk, in which 

 the large spheroidal germinal vesicle is enclosed ("nucleus," yn). It contains a visibly 

 dark, germinal spot (" nucleolus," yf), and this again contains a large double contoured 

 germinal point (" nucleolinus," fig. 4, yp). 



Order VIII. CUBOMEDUS^E, Haackel, 1877. 



Acraspedse with four perradial sense clubs, containing an auditory club with 

 endodermal otolite sac and one or more eyes ; four interradial tentacles or bunches of 

 tentacles. Stomach with four wide perradial quadrangular pouches separated by four 

 long, narrow interradial septa or fused selvages. Genitalia four pair of leaf-shaped swell- 

 ings, which are fastened by one margin along the four interradial septa, are developed 

 from the subumbral endoderm of the gastral pouches, and project freely into their hollow 

 space. 



Family Charybdeid^e, Gegenbaur, 1856. 



ChArybdeid.e, Hasckel, System der Medusen, 1879, p. 433, taf. xxv. 



Cubomedusas with four simple, interradial tentacles and four perradial sense clubs ; 

 without marginal lobes in the velarium, but with eight adradial marginal pouches ; with- 

 out pouch arms in the four broad perradial pouches. 



Sub-family, Tamoyid^:, Hseckel, 1877. 

 Charybdeidaa with velar canals, and with four perradial frenula of the velarium. 



Charybdea, 1 Peion and Lesueur, 1809. 



Charybdeidas with four simple interradial tentacles, having pedalia ; with suspended 

 velarium (with velar canal and four perradial frenula). Stomach flat and low, without 



1 X«pi;/35is = an eddy, a gulf, rapacious. 



