THUIARIA THUJA. 275 



stage. On fixing themselves, they assume the usual circular 

 form ; the stem soon begins to rise in the centre of the disk, 

 and the marginal portion is broken up into a number of 

 rays, which, like so many root-fibres, bind the shoot to its 

 place. These may still be traced in the adult condition. 



In the young state the calycles are bent alternately in 

 opposite directions; but there is no departure from the 

 strictly unilateral arrangement (Plate LVIII. fig. c}. 



When dried, the branches of H.falcata become recurved, 

 and assume the sickle-like appearance from which the 

 specific name is derived. 



Hob. On shells and stones, in the coralline zone, uni- 

 versally distributed. 



[Ostend, extremely common (Van Ben.) : Mingan Island, 

 Gulf of St. Lawrence (teste A. S. Packard, jun.): Grand 

 Manan; taken often in 35 fath. on the Hake-ground 

 (Stimpson): Massachusetts Bay (Agass.): South Africa 

 (Busk).] 



Genus THUIARIA, Fleming. 



Der. from 9 via, a cedar. 



GENERIC CHARACTER. Zoophyte plant-like ; stem branch- 

 ing, jointed, rooted by a filiform stolon ; hydrotheccs bise- 

 rial, imbedded in the substance of the stem and branches. 



THUIAXIA is most closely allied to Sertularia ; but the ap- 

 pression and partial immersion of the calycles give it a pe- 

 culiar and very distinctive aspect. Few species are known. 



1. T. THUJA, Linnaeus. 



" BOTTLE-BRUSH CORALLINE," Ellis, Corall. 10, pi. T. figs, b, B. 

 SERTULARIA THUJA, Linn. Syst. 1308; Pallas, Elench. 140; Esper, Pflanz. 



Sert. t. xxii. figs. 1-3 ; Lama-. Cor. flex. 193. 

 CET/LARIA THUIA, Lamb. An. a. Vert. (2nd ed.) ii. \Ki. 



T2 



