146 PEOP. A.LLMAN ON NEW HTDEOIDA PROM 



transparency of its chitinous periderm and for its large cylindrical 

 plicated gonangia, which in tlie specimen examined were profusely 

 developed along the upper side of the pinnge. The contents of 

 the gonangium were always accumulated as an opaque brown 

 mass in the top of its cavity ; the plication of its walls was here 

 most distinctly marked, and before reaching the base became 

 obliterated. The species has been examined by Mr. Busk, but 

 not previously described. 



Thfiaeia bamosissima, n. sp. (PL XYIII. figs. 4, 5.) 



Trophosome. — Hydrocaulus monosiphonic, main stem sending 

 off in every direction branches which are themselves profusely 

 branched ; ramification subdichotomous, each bifurcation preceded 

 by a transverse joint. Hydrothecse alternate, adnaie to the 

 hydrocaulus by the whole of their epicauline walls, deep, tubular ; 

 the apocauline margin of aperture deeply cleft. 



Gonosome. — Gronangia springing each from a point placed 

 laterally just below the base of a hydrotheca ; none mature in 

 the specimen. 



Locality. North-east coast of America. 



The profuse ramification and beautifully plumose disposition 

 of the branches constitute a striking feature in this fine species. 

 In the dried specimen the main stem is brown, while the branches 

 are of a remarkable pale green. The specimen, which is somewhat 

 more than 2 inches in length, has been broken off" from the distal 

 end of the colony, and we have no exact data for determining the 

 actual height attained by the species. Some gonangia, too young 

 to allow of the characterization of the mature form, were present 

 in the specimen, where they sprung each from a point just below 

 the base of a hydrotheca. 



Thuiaeia Hippisleyana, n. sp. (PI. XIX. figs. 1-3.) 



Trophosome. — Stem simple, monosiphonic, set with piunately 

 disposed, opposite, unjointed ramuli along nearly its entire length. 

 Hydrothecse borne both by stem and pinnse, deep, nearly cylin- 

 drical, aduate to stem and pinnse for their entire height, alternate 

 and closely set on the pinnse, nearly opposite and more distant 

 on the stem, marked towards the base with longitudinal undu- 

 lating and prominent strise ; margin of orifice crenate, and with a 

 deep sinus at its epicauline side. 



Gonosome not known. 



Locality. Australia. 



This is a beautiful and well-marked form. It attains a height 



