RHIZOSTOM^. — HIIoriLKMA. 707 



ofthe subumbrella consists of i6 triangular areas which alternate with and are widely separated 

 by the 1 6 radial-canals. 



This medusa was described In' \ aiihoffen from Hongkong;, China, and later by Maas 

 from the Malay Archipelago. It appears to be identical with R. vfrrucosti Kishinouye, from 

 Japan. R. hispiJunt is possibly identical with Pilema clavigcra Haeckcl; but in Haeckel's 

 medusa there are only 48 marginal lappets when the disk is go mm. wide, whereas in R. 

 htsptdum of the same width there are 80 marginal lappets. The granular projections upon 

 the exumbrella in Haeckel's medusa are bluntly rounded, whereas in R. hispiJuni thev are 

 sharp and thorn-shaped. The terminal appendages of the mouth-arms appear to be some- 

 what longer in Haeckel's medusa than in R. hispulmn. Hacckel describes " Pilerna clavigera" 

 from a single alcoholic specimen from Hongkong, China. 



Rhopilema verrillii. 



Plate 74, figs. I, I'. 

 Nectopilema verrillity Ff.wkks, 1887, American Journ. Sci., ser. 3, vol. 3^, p. 119, plate 4. 



The disk is tuUy 350 mm. in diameter, hemispherical in contraction, but slightly flatter 

 than a hemisphere when expanded. The gelatinous substance is thick and rigid. The cen- 

 ter of the exumbrella is smooth, but over the lappets there are many shallow furrows and 

 the surface near the margin resembles sand-paper, being covered with numerous minute ele- 

 vations. There are 8 marginal sense-organs, each of which contains a terminal, entodermal 

 concretion-mass of red pigment granules. There is a simple, exumbrella sensory pit without 

 furrows; 64 marginal lappets. There are 6 large, oval lappets in each octant ot the margin ot 

 the disk, together with 2 small, oval lappets adjacent to the sense organs. 



The arm-disk is cruciform and about half as wide as the bell, and the 4 perradial col- 

 umns are only three-fifths as wide as the heart-shaped, subgenital ostia. 8 short, tough, 

 gelatinous, lower mouth-arms, which arise from the arm-disk, are each about 180 mm. long 

 and Y-shaped in cross-section below. They branch sparingly and the very numerous mouths 

 are found upon their lower and inner sides, in furrows bordered by numerous, small, waving 

 cirri. There are about 25 to 60 blunt, translucent spindle-shaped appendages, which arise 

 from the lower sides of the mouth-arms, and are besprinkled with wart-like clusters ot 

 nematocysts. The largest filaments arise from the principal crotches ot the mouth-arms. 



A pair of short flapper-like, lateral scapulets arise from the outer side of each ot the 

 8 mouth-arms near its base, the mouth-openings of which are confined to their upper edges 

 and connect by a main duct in each scapulet with the axial-canal ot the arm to which they are 

 attached. There are no appendages upon the scapulets. 4 short, gelatinous, perradial columns 

 connect the arm-disk with the subumbrella. There are 4 deep, heart-shaped clefts or genital 

 ostia between these 4 columns, but the bottom of each cleft is bridged over by a delicate 

 membrane. The 4 separate gonads develop within this membrane and the stomach is bor- 

 dered on the sides by the 4 stout, perradial columns and the 4 interradial membranes. 

 The 4 genital sacs are separated one from another; indeed the gonads are somewhat protru- 

 sive in old medusae. 



There is a blunt wart-like papilla upon the subumbrella surface at a short distance 

 beyond the opening of each genital ostium, and this panially constricts the opening, giving 

 it a heart-shaped outline. The circular muscles of the subumbrella are very powerful, but 

 are almost interrupted in the radii ofthe 16 radial-canals in old medusje although they are 

 entire near the margin in young animals. Thus in old medusa; there are 16 partially isolated 

 arcades of circular muscles as in Rhizostoma pulmo. There are no radial muscles. 



The stomach is wide and cruciform, and corresponds in outline with the cruciform 

 arm disk under which it lies. Its exumbrella roof is plane, but the subumbrella floor dips 

 downward into the center ofthe arm-disk, and 4 open, perradial, gutter-like furrows extend 

 from this central depression down the center of each perradial column to the outer edge ot 

 the stomach. 4 perradial ducts arise from the depressed center of the stomach at the 

 middle ofthe arm-disk, and these soon bifurcate giving 8 adradial ducts which extend down 

 each ofthe 8 mouth-arms giving offside branches to the numerous mouths. 



