28 THUIARIA SERTULARIOIDES. 
Thuaria plumulfera has a good deal of the habit of Hydrallmaua falcata. 
The pinna-bearing branches are regularly divided into equal internodes, 
each internode carrying three hydrothece and giving off a pinna from 
alternate sides just above its proximal end. The pinnez are much contracted 
at their origin, and united to the branch which carries them by a very short, 
nearly globular internode. The joints of the pinne are at distant and 
uncertain intervals. 
The hydrothecx at their distal ends are thin and collapsible, so that it 
was very difficult to determine the true form of the orifice. In some cases, 
however, where the parts were well preserved, it could be seen that the 
thin collapsible portion was a tubular prolongation of the walls beyond 
the true orifice, which was provided with two strong, broad lateral teeth. 
The gonangia had all fallen, but the indications of their attachment 
were visible just below many of the hydrothece. 
Thuiaria pinnata. 
Pl, XV. Figs. 1, 2. 
Trophosome.— Stem attaiing a height of nearly three inches, sparingly 
branched, fascicled below, alternately pinnate; pinne given off at nearly 
right angles to the stem, jointed at distant and uncertain intervals. 
Hydrothec borne both by stem and pinne, deep cylindrical with 
obscurely 4-toothed margin, adnate to the axis in their whole length. 
Gonosome not known. 
Double-headed Shot Key from a depth of 3 to 4 fathoms. 
Thuuria pinata is a strong, rather rigid form, rendered somewhat 
striking by the very open angle at which the pinne are given off from 
the stem. Some of the hydranths were well preserved in the speci- 
men, and it would appear that they are capable of extending them- 
selves far beyond the orifice of the hydrotheca. 
Thuiaria sertularioides. 
Pl. XVI, Figs, 115 as 
Trophosome. —Hydrocaulus attaining a height of three inches, slender 
cylindrical, sending off short, simple branches which spring from the 
anterior aspect of the axis. Hydrothecx opposite, with the distal half 
free and divergent, gradually narrowing from the base to the orifice, 
