1906.] MR. E. S. RUSSELL ON A NEW HYDROID. 99 



4. On TrichorJdca, a new Hydroid Grenus. 

 Bv E. S. Russell*. 



[Received November 11, 1905."] 

 (Plate Y. t) 



Trichorhiza, 



Hydranth solitary, attached loosely by the hydrorhiza, which is 

 filiform and branched. Invested by perisarc, which forms a 

 protective cup into which the hydranth is partly retractile. 



The genvis Trichorhiza is here constituted for a single new 

 species, whose characters are so remarkable as to make the 

 formation of a separate genus for its reception a necessity. The 

 following description of this new species is made from the only 

 specimen which I have seen. 



Trichorhiza buunnea. (Plate V.) 



Trichorhiza hrunnea Russell, Abstr. P. Z. S. JSTo. 26, p. 6, Feb. 13, 

 1906. 



Trophosome. Hydrorhiza long and tapering, giving off about 

 half-a-dozen filiform branches along the lower half. The coenosarc 

 apparently does not extend into this lower half nor into the 

 branches. The perisarc expands above to form a cup, marked by 

 four transverse grooves. Immediately below this cup several 

 longitudinal lines are present on the perisarc. The hydranth is 

 conical upon a moderately long peduncle. Tentacles in two verticils ; 

 the proximal filiform, twelve in number, when extended as long as 

 the hydranth, set with numerous rings of nematocysts ; the distal 

 capitate, seven in number, and very short. The latter are 

 inserted on the summit of the hypostome, the former near the 

 base of the conical head of the hydranth. 



Gonosome. A circlet of 8-10 sessile medusoids, which are 

 developed between the proximal and the distal rows of tentacles 

 and become free. 



Dimensions : — 



Total length of hydranth 1 • 5 mm . 



Total breadth of hydranth 0*8 mm. 



Overall length of hydroid 1 1 "0 mm. 



Colours. Perisarc straw-coloured, except that forming the cup, 

 which is chocolate-coloui'ed. Tentacles translucent white. Body 

 of hydranth pale reddish-brown. 



Gonophore (at time of liberation). Hemispherical, in systole 

 bell-shaped, slightly contracted in the upper third, and constricted 



* [The complete account of the new species described in this commnnication 

 appears here ; but since the name and preliminary diagnosis were published in the 

 'Abstract,' the species is distinguished by the name being underlined. — Editoe.] 



t For explanation of the Plate, see p. 101. 



7* 



