ANTHOMKOrs.K STVI. UTIS, TH \ M \( ISTV I.I'S. I .") I 



There is no hydrocaulus. The hydrorhiza is a network of tubes lying in one plane, from 

 which arise a tew small, simple spines and many sessile h\ dranrhs. The hydranths are of 

 two kinds, nutritive and reproductive. The nutritive hvdranths are ahout 25 mm. long and 

 are elongate, simple, and unbranched. Their oral ends taper gradually, being widest at the 

 circlet ot tentacles. There are usually about 20 long, slender tentacles arranged in a single 

 whorl, but specimens are found with as many as 35 and as few as 15 tentacles. The entoder- 

 mal cores of these tentacles are solid and consist of a single row of cells. The tips of these 

 tentacles are not appreciably swollen or knob-like, although they are well provided with 

 nematocysts. 



The reproductive hydranths are slightly smaller than the nutritive ones. They have 

 only 6 to 10 tentacles and are only one-third to three-fourths as long as the nutritive hydranths, 

 but they have functional mouths. 1 here are usually 4 to 5 medusa-buds arranged in a circlet 

 immediately below the circle of tentacles. The entoderm of the hydroid is white or pinkish- 

 white. The medusae appear to be set free soon after dark, and the breeding season extends 

 throughout July and August. 



There are no spiral protective zooids such as are found in Hydractinia and there is no 

 coenosarc layer over the hydrorhiza such as is found in H \Jrtu tnnn and l ) 'iJ(n-r>r\>if. 



Stylactis arge Clarke. 

 Xijiiilis argt, CHRKK, |S82, Mem. Boston Soc. N.u. Hi^t., \.,l. ;, p. i ^K, plate 8, figs. 18-20. 



The medusiform gonophores of this species often become mature while attached to the 

 hydroid stock. In other cases, however, the gonophores become free, although they are 

 sexually mature at the time of liberation. 



hit-f medusa. The bell is ellipsoidal and the gelatinous substance thin. There are 8 

 small rudimentary tentacle-bulbs, 4 radial and 4 interradial. 4 simple, narrow radial-canals. 

 1 he manubnum is globular and greatly distended by the contained genital products. 



Hydroid. The hydranths are very much elongated and slender. Kach Indranth is 

 provided with 10 to 30 tentacles which arise in 2 circlets close together below the lupostome. 

 The tentacles ot the lower circlet are somewhat shorter than those of the upper one, although 

 in some individuals all ot the tentacles are of equal length. There are usually 4 sporosacs or 

 medusa-buds developed upon the sides ot the body ot the hydranth beneath the circlets of 

 tentacles, 2 being first developed on opposite sides ot the hydranth, and then 2 others appear 

 at points 90 from the first pair. The entire colony is of a delicate opaque white. 



It is remarkable that in this species a constriction sometimes appears around the hodv 

 ot a hydranth, from a point just above which two or three cylindrical, stolon-like processes 

 are developed. The constriction then becomes complete and the distal end ot the hydranth 

 becomes tree. This then settles down in a new locality and the stolon-like processes give 

 rise to a hydrorhiza and a new colony is thus developed asexually. 



This species has been found by Clarke in Chesapeake Bay. 



Genus THAMNOSTYLUS. 



Thardnostylut, H\K KM., 1X74, Syst. lrr iUfilusrn, p. S^; iSSl, Rrpnrt H. M. S. ('.l tl ill-'n ^ > . '/.'}., \ol. 4, p. z. 



The only known species is Thamnostylui Jnh'nni llaeckel, from the Antarctic Ocean. 



GKNKRIC CHARAC I I RS. 



Margelinz with branched oral tentacles and 2 marginal tentacles iSo" apart. Develop- 

 ment unknown. 



Thamnostylus dinema Haeckel. 



Thamnostylui <ltnetmi, HAH KM, 1^7*), S\st. *!i-r Mrdusrn, p.N>; iXSi, Report H. M. S. (:imll>-ny, /.o<,l., vnl. 4, p. 2, pl.itr i, 

 8 figs. 



Bell hemispherical, ]<i mm. wide, S mm. high, with thick gelatinous substance, but 

 thin at margin. The margin is thickly studded with nematocvsts and the exumbrella is .I!M> 

 besprinkled with isolated nettling cells. 2 diametrically opposite, radiall) situated, hollow. 



