MAYER : MEDUSAE FROM THE TORTUGAS, FLORIDA. 35 



GEMMARIA, McCradt, 1857. 

 Gemmaria dichotoma, nov. sp. 



Fig. 40, Plate 17. 



Specific Characters. — The bell is 3 mm. in height and there is a solid mitre- 

 shaped apical projection. The bell walls are thin. There are two rudimentary 

 tentacle bulbs and two well-developed tentacles. The entodermal core of 

 these large tentacles is hollow. They terminate in a bulb-shaped nematocyst 

 swelling, which in some individuals is provided with delicate bristles. A 

 number of tentaculse arise from the upper or " dorsal " side of the tentacle, 

 and each one of these terminates in a bulb-shaped swelling similar to that at 

 the distal end of the main tentacle. The youngest and least-developed of 

 these side branches is always found nearest the bell. The basal bulbs of the 

 tentacles are large, and there is a single deep red ocellus in the outer surface of 

 the ectoderm of each. The velum is quite well developed. There are 4 

 straight radial canals and a narrow circular canal. The proboscis is pyrifonn 

 and extends about half the distance from the apex of the bell cavity to the 

 velar opening. The entoderm of the proboscis and tentacles is ochre-yellow. 

 Several specimens were found at the Tortugas early in July. 



Gemmaria gemmosa, McCrady. 



Fitjs. 137, 138, Plate 41. 



Gemmaria gemmosa, McCrady, J., 1857, Gymn. Charleston Harbor, p. 49. 

 Zanelea gemmosa, McCrady, J., 1857, Gymn. Charleston Harbor, p. 48, PI. 8, 

 Figs. 4, 5. 



Specific Characters. — Hydroid stock ; Gemmaria gemmosa. The hydroid 

 was found at the Tortugas, Florida, growing upon a piece of floating gulf- 

 weed (Sargassum). The hydrorhiza is creeping and net-like, and gives rise at 

 irregular intervals to short, more or less twisted hydrocauli. Both the hydro- 

 rhiza and hydrocauli are covered with a horny, chitinous perisarc, which in 

 the hydrocaulus displays a number of annulations. The hydrocaulus is corru- 

 gated, and opaque in color, throughout its length ; and in this respect differs 

 from the European G. implexa described by Allman (1871, Tubulariaii 

 Hydroids, p. 290, Plate VII.). The fully developed hydranths are only 1.5 

 mm. in height. They are elongate, and the diameter near the proximal end is 

 a little greater than at the free oral extremity. The tentacles arise in 5-8 

 whorls from the side of the hydranth. Each whorl contains 4-6 short tentacles. 

 Each tentacle terminates in a distal knob which is armed with a dense cluster 

 of nematocysts. The cells of the shafts of the tentacles are vacuolated, and 

 the tentacles themselves quite stifi" and inflexible. 4-8 medusa-buds arise from 

 the side of the hydranth immediately below the proximal whorl of tentacles. 



