EEPOET OX THE HYDEOIDA. 
43 
As in the other species of Cryptolaria in which the gonangia have been found, these 
receptacles spring from the axial tube where this is covered by the peripheral, and 
have their distal ends curving away from the stem. In Cryptolaria diffusa, how- 
ever, they present the singular feature of being sometimes geminate, while this 
condition is found on the same branch which carries the ordinary solitary form of 
gonangium. The geminate gonangia spring from a very short common peduncle, 
and immediately become adherent, back to back, for about three-fourths of tlieir 
height, the distal fourth being free and divergent. It is impossible with our present 
knowledge to assign with confidence any reason why there should be this difference in 
the gonangia of one and the same colony. If it be not an abnormal occurrence of merely 
individual significance, it may possibly point to a monoecious condition of the colony, 
involving a sexual difference between the solitary and geminate gonangia. 
Pcrisiphonia, n. gen. 
Name from ~ep\, around, and o-ujW, a tube, in allusion to the way in which the axial tube is 
surrounded by the peripheral ones. 
Generic Character. Trophosome. — Hydrocaulus composed of two constituents, an 
axial and a peripheral ; the axial formed by a continuous tube which carries at intervals 
along its length pedunculated hydrothecae ; the peripheral formed by numerous tubes which 
completely surround the axial in its entire length, are destitute of hydrothecae, but allow 
the hydrothecae of the axial tube to project through interstices between them into the sur- 
rounding water ; the superficial tubes of the peripheral fascicle set with tubular sarcothecae. 
This remarkable genus has very obvious affinities with Cryptolaria, from w T hich, 
however, it essentially differs in its hydrothecae being provided with well-defined 
peduncles, instead of having their cavities directly continuous with that of the tube from 
which they spring, in the axial tube never becoming free from the cover of the peripheral, 
and in the presence of a well-developed system of sarcode-bearing receptacles. 
In Perisiphonia fflicula and in Perisiphonia pectinata, the only two species as yet 
known, the hydrothecae are flask-shaped and are disposed alternately in regular sequence 
along the entire length of the axial tube. The peripheral tubes completely envelop the 
axial, are continuous throughout the entire length of the branch, and although separable 
as in the other Perisiphonidae, are adherent to one another except at the places through 
which the ends of the hydrothecae protrude. Hence no part of the axial tube becomes 
exposed as in Cryptolaria, the peripheral tubes continuing to invest it to the extreme 
ends of the branches. 
Another very remarkable feature in Perisiphonia consists in the presence of minute 
tubular receptacles which are borne by the superficial tubes of the peripheral fascicle. 
In both species these are carried all along the length of the tubes, and under a low 
