152 MEDUS.E OF THK WOULD. 



marginal tentacles about 3 times as long as the bell-diameter and ringed at frequent inter- 

 vals with swollen masses oi" nematocysts. The basal bulbs of these tentacles are swollen 

 and conical and each one bears a dark-red abaxial ocellus. There are 2 rudimentary, ocellated 

 tentacle-bulbs upon the margin 90 apart from the long tentacles. Velum wide. 4 straight, 

 narrow radial-canals and a simple ring-canal. 



The stomach is a wide, 4-sided pyramid, as long as the depth of the bell-cavity. It extends 

 below into a 4-sided, elongated throat-tube, twice as long as the stomach itself. This throat- 

 tube projects beyond the velar opening and the mouth is a simple, 4-sided opening studded 

 with nematocysts. 



4 large, radially placed, oral tentacles arise from the distal end of the stomach and branch 

 dichotomously 6 to 8 times, their ends terminating in nematocyst-knobs. The gonads are 

 swollen, leaf-like, lobular, folded ridges in the 8 adradii of the stomach. They are blunt 

 above, but more pointed below, and each gonad exhibits about 5 double transverse folds. 

 The ova are prominent. The gonads, oral tentacles, nematocysts of bell-margin and of the 

 tentacles and tentacle-bulbs are blood-red. 



Antarctic Ocean, south of the Kerguelen Islands, at a depth of 120 fathoms. Beautifully 

 figured by Haeckel, 1881. 



Genus THAMNITIS Haeckel, 1879. 



Thamnitis, HAF.CKEL, 1879, Syst. der Medusen, p. 84. VANHUFFF.N, 1891, Zool. Anzeigcr, Bd. 14, p. 444. BROWNE, 1905, Proc. 

 Royal Soc. Edinburgh, vol. 25, p. 758. 



The first described species of this genus is Thamnitis nigritella, first made known by 

 Forbes, 1848, under the name Bougainvillea nigritella. The first species mentioned by 

 Haeckel is a newly-described form, Thamnitis tctrclla. T. nigritella comes from the Shetland 

 Islands, while T . tctrclla was obtained off the coast of Brazil. 



GENERIC CHARACTERS. 



Margelinae with branched oral tentacles and 4 simple, radially placed, marginal tentacles. 



It is possible that Thamnitis may be simply an immature or damaged Bougainvillia 

 which has lost all but one marginal tentacle of each radial cluster, but we are not yet justified 

 in concluding that this is the case. Forbes, 1848, describes and figures the tentacle-bulbs of 

 Thamnitis nigritella as being bean-shaped, containing a single large ocellus ( ?) or mass of 

 very dark pigment, and having a single short tentacle arising from one side of the bulb, not 

 from the middle. Haeckel, 1879, p. 84, describes T. tctrclla as having small, pear-shaped ten- 

 tacle-bulbs with a single tentacle arising from the middle of each bulb. He does not mention 

 ocelli, but his description is brief and unaccompanied by a figure. Further study is required 

 before we can be certain that T hamnitis actually exists in nature. Vanhoffen, 1891, accepts 

 it with some hesitation, and I share his view in this respect. 



Browne, 1905 (Proc. Roy. Soc. Edinburgh, vol. 25, p. 758), is the only recent author 

 who has seen a specimen of Thamnitis. He found two small, immature medusae in the Firth 

 of Clyde, Scotland, in September to October. They were I to 1.5 mm. wide and had 4 simple, 

 marginal tentacles. No ocelli. 4 oral tentacles 2 to 3 times dichotomously branched. No 

 gonads. Stomach yellow to orange, tentacle-bulbs orange. 



"Thamnitis nigritella" Forbes, 1848 (British Naked-eyed Medusae, p. 63, plate 12, 

 fig. 2) is probably an immature Bongainvillia which has lost all but one tentacle in each 

 marginal cluster. 



Thamnitis tetrella Haeckel. 



Thamnilii lelrel/a, HAECKF.L, 1879, Syst. der Medusen, p. 84. 



Bell egg-shaped, being 6 mm. in height and 4 mm. in diameter. There are 4 radially 

 situated, marginal tentacles which are longer than the bell-height. Each tentacle arises from 

 the middle of a large basal bulb. An ocellus is situated at the base of each tentacle. There 

 are 4 radial-canals. The manubrium is cubical with a wide quadratic base. There are 4 

 radially situated, oral tentacles, each of which branches dichotomously three times. The 

 gonads are found in 4 interradial ( ?) swellings upon the wall of the stomach. Color ( ?) 

 This species is found upon the coast of Brazil. 



