Prof. Allman on the Hydroida. 57 



Ylll.— Notes un the Hydroida. By Prof. Allmax, F.R.S. 



I. 



Note, ntpplemental and corrective, to a Synopsis of the Genera 

 and Species of Tubularian and Campamdarittn Hydroids, published 

 in the 'Annals and Magazine of Natural History' for May ISC-l-, 

 p. 350. 



[Plate II.] 



Perigommus vestitus, AUman, n. sp. * 



Drophosome. — Hydrocaulus composed of numeroua Rtems, 

 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 a(lh< 

 particles of sand. Polypites with from six to ten tcntai - 

 which are roughened by irregularly annular groups of minute 

 thread-cells, and in extension are usually held with the alter* 

 Date 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 tcnninating 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 ^urctniim-shell, where it was asso- 

 ciated with Hydracdnia echinota. 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 Perigomimmt vtttitut and Tmbularie k umH it, 

 which are now recorded for the first time, all the species here described 

 will be found under their respectiTC eenera in the Synopsis, where, how- 

 ever, they are simply enumerated, without any description. 



