REPORT ON THE HYDROIDA. 
45 
at the points where they leave the peripheral fascicle that they show any decided 
approximation to an opposite disposition. 
Under a low power the whole surface may be seen to be thickly studded with the 
little tubular sarcothecae, which constitute so remarkable a character of the genus. 
The hydrothecas project but slightly from the surface and are regularly alternate and 
distichous, with entire circular orifice. When the axial tube of the stem is carefully 
exposed by the removal of the investing peripheral tubes, it will be seen that close to the 
base of several of the hydrothecal peduncles a branch is sent out at nearly a right angle 
from the main tube, from which it scarcely differs in thickness. Some of these branches 
soon terminate abruptly, while others are continued beyond the peripheral fascicle, bear 
pedunculated hydrothecae, and constitute the axial portion of a lateral ramulus or pinna. 
This becomes surrounded by a fascicle of peripheral tubes, which are given off from the 
peripheral tubes of the stem. The peduncle of every hydrotheca carries a sarcotheca 
similar to those of the peripheral tubes, while two or three similar bodies are also 
frequently borne by the lateral offset near its base. The peripheral tubes terminate at 
the distal end of the ramuli in truncated but apparently closed extremities, and no part 
of the axial tube is here exposed, as is always the case in Cryptolaria. 
The walls of the peripheral tubes are much thinner than those of the axial, and 
under the action of certain reagents, as caustic potash, shrivel and collapse, while the axial 
tube retains almost completely its original form. About ten tubes usually enter into the 
composition of the peripheral fascicle of a pinna. 
Perisiphonia pectinata, n. sp. (PI. XXI. figs. 2, 2a, 26). 
Trophosome . — Colony with the main stem sparingly branched, attaining a height of 
about five inches, stem and branches thick, carrying pinnately disposed, equidistant, 
nearly opposite, slender ramuli. Hydrothecae flask-shaped, curved away from the axial 
tube, and with the neck rather long and slender. 
Gonosome not known. 
Locality . — Station 169, off New Zealand; lat. 37° 34/ S., long. 179° 22 ; E.; depth, 
700 fathoms. 
The very regular, nearly opposite, disposition of the ramuli in this species is 
accompanied by a somewhat rigid habit, which gives a pectinate aspect to the branches. 
The more elongated and more slender neck of the flask-shaped hydrothecae, and its 
greater extension beyond the surface of the peripheral fascicle, are among the characters 
which distinguish Perisiphonia pectinata from Perisiphonia Jilicula. Another point in 
which the present species differs from Perisiphonia Jilicula will be found in the greater 
slenderness of the pinnately disposed ramuli, which have here not more than half the 
diameter of these ramuli in Perisiphonia Jilicula. The slenderness of the pinnae in 
