36 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



When set free the young medusa possesses 2 well-developed diametrically- 

 opposed tentacles and 2 rudimentary tentacle bulbs (Figure 137). The 4 

 radial, nematocyst-bearing swellings upon the ex-umbrella extend halfway up 

 the sides of the bell from the margin toward the apex. The bell walls are 

 uniform, and very thin and flexible. There are 4 slender radial canals, and 

 the proboscis is a short simple tube with no trace of gonads. Before being set 

 free, the tentacles are carried coiled inward so that they lie protected within 

 the bell cavity. Soon after liberation, however, the tentacles are turned out- 

 ward. (Compare Figm-es 137 and 138.) The deep-lying entoderm of the 

 hydranth is of a delicate creamy pink, while the more superficial entoderm is 

 of a translucent milky color. The entodermal cells of the superficial entoderm 

 are large and vacuolated. The hydrorhiza is of a horny yellow color. This 

 species is quite different from Gemmaria imyjlexa of Allman. It is probably 

 the hydroid of Zanclea gemmosa, McCrady, of Charleston Harbor, but not 

 having been able to raise the medusae we must remain in some doubt concern- 

 ing its identity. 



NIOBIA, nov. gen. 

 Niobia dendrotentacula, nov. sp. 



Figs. 141-143, Plate 42 ; Fig. 144, Plate 43. 



Generic Characters. — Niobia. Cladonemidse with 2 simjile and 2 bifurcated 

 radial canals. There are 4 simple lips to the proboscis, but no oral tentacles. 

 The marginal tentacles develop into free-swimming medusa?. 



There is no place in the system of Haeckel (1879; p. 101) for this genus. It 

 cannot be placed among the Dendronemidse, for it has no oral tentacles, and as 

 it has branched radial canals it cannot be classed among the Pteronemidse. It 

 combines the essential characters of both of these subfamilies, however, and 

 forms a good connecting link between them. 



Specific Characters. — Adult medusa. The bell is slightly flatter than a 

 hemisphere, and is about 4 mm. in diameter. The gelatinous substance is 

 quite thin and uniform, but not very flexible. The tentacles are arranged in 

 bilateral symmetry, the axis being in the diameter of the two simple radial 

 canals (see Figure 144, Plate 43). The oldest tentacle is situated at one end, 

 and tlie youngest at the other end of this axis. (Figures 142, 144.) Each lialf 

 of the medusa is a reflection of the other, and the order in age of the tentacles 

 is given by the following diagram, the oldest tentacle being numbered (1) and 

 the youngest (7) : — 



