Prof. Allman on the Hydroida. 57 
VIII.—Notes on the Hydroida. By Prof. Atuman, F.R.S. 
i 
Note, supplemental and corrective, to a Synopsis of the Genera 
and Species of Tubularian and Campanularian Hydroids, published 
in the ‘Annals and Magazine of Natural History’ for May 1864, 
p. 350. 
[Plate II. | 
Perigonimus vestitus, Allman, n. sp.* 
Trophosome.—Hydrocaulus composed of numerous stems, 
from half a line to two lines in height, becoming greatly dilated 
towards the summit, simple or occasionally with one or two 
short lateral branches, and connected by a delicate creeping and 
retiform hydrorhiza; periderm yellowish brown, with adherent 
particles of sand. Polypites with from six to ten tentacles, 
which are roughened by irregularly annular groups of minute 
thread-cells, and in extension are usually held with the alter- 
nate ones elevated and depressed ; a delicate continuation of the 
periderm extends over the whole of the body of the polypite 
beyond the tentacles, and almost to the margin of the mouth ; 
this peridermic covering, however, is not continued over the 
tentacles, but becomes lost on their roots. 
Gonosome.—Gonophores elevated on long peduncles, which 
spring from the hydrocaulus and occasionally also from the hydro- 
rhiza, the peduncle for about its proximal half being invested by 
a continuation of the opake chitinous periderm. Medusa, at 
the time of liberation, oviform, the cavity of the umbrella being 
very deep, and the umbrella-mouth (“ codonostome”) much 
contracted ; umbrella-walls very thin and with minute scattered 
thread-cells immersed in them; two opposite marginal tentacles 
with non-ocellated bulbous bases, the intervening radiating 
canals terminating each in a smaller bulb, from which no tentacle 
has been developed; manubrium with four shallow lips. 
Perigonimus vestitus was met with in the Firth of Forth in 
June, growing upon an old Buccinum-shell, where it was asso- 
ciated with Hydractinia echinata. In the continuation of the 
periderm over the body of the polypite, as well as in general 
habit, it comes very near to the Perigonimus (Atractylis) palliatus 
of Wright, from which, however, it differs, judging from Dr. 
Wright’s description and figures, in its more developed hydro- 
caulus, in the position of the gonophores—which are here borne 
* With the exception of Perigonimus vestitus and Tubularia humilis, 
which are now recorded for the first time, all the species here described 
will be found under their respective genera in the Synopsis, where, how- 
ever, they are simply enumerated, without any description. 
