314 EENEST WARREN. 



liydroid grows plentifully on tlie sea-weeds of the rock-pools. 

 It is also stated to be the rule for the lowest internode to bear 

 only a single part of hydrothecfB ; in the Natal hydroid this 

 is the exception, as there are generally two pairs. 



The presence of the characteristic pegs or ribs of perisarc 

 extending into the hydrorhiza is not mentioned by Nutting, 

 and it is possible that the Natal hydroid is peculiar in possess- 

 ing them; and should such be the case the character is sufficient 

 for founding a variety or even a new species. 



(21) Thuiaria tubuliformis [Marhtanner-Turneretscher). 



Dynamena tubuliformis Marhtanner-Turneretscher. 'Hydroid desk. 



k. natm-. H. of Museums/ 1890, p. 238. 

 Thuiaria tubuliformis (Marldanner-Tiirneretscher). Nutting, C. C, 



' American Hydroids,' pt. ii, " Sertu- 



lariida;," 1904, p. 70. 



This hydroid is one of the commonest on the Natal coast. 

 It occurs on worm-tubes, and also attached to the vertical 

 sides of rocks which are left bare during low-tide. Very 

 probably, in deeper and quieter water, it has a more luxuriant 

 habit; but in such positions as it has been found it rarely 

 attains to more than an inch in height. It is of a pale 

 yellowish-brown colour. The reproductive bodies are only 

 rarely found. 



The identification of the hydroid with T. tubuliformis 

 has been made from Nutting's description. 



Trophosome. — Hydrorhiza, creeping stolon irregularly 

 branched. 



Diameter 0'263 mm., thickness of perisarc IS fx. 



Hydrocaulus. — Stems reach about 1 inch in height, 

 ziz-zag, bearing alternating branches, divided into regular 

 internodes, each bearing a branch and two hydrothecae on 

 one side, and a single hydrotheca on the other (text-fig. 12, C). 

 Branches are divided into irregular internodes, and are con- 

 stricted at their origins. 



