HALATRACTUS NANUS. 391 



bell-shaped, witli one of the four radiating canals continued into a short club-shaped 

 tentacle, while each of the others terminates at the margin of the umbrella in a bulb 

 destitute of tentacle ; manubrium long-, with a simple mouth. 



The genus Ilulutradus has been instituted for the Cori/morplia nana of Alder, whose sessile 

 gonophores at once distinguish it from the true Corymorphas, whose gonophores are always pedun- 

 culated. Alder, however, in his description of this bydroid, mentions another character, which, 

 if established, would be one of great importance ; for he tells us that while the gonophores are 

 jdiauerocodonic in some individuals, they are adelocodonic in others, and he figures irrcgularly- 

 lobed oval bodies as tlie adelocodonic form, suggesting at the same time that this condition may 

 depend on a difference of sex. 



The peculiarity thus indicated I cannot accept without the confirmation which the examina- 

 tion of a greater number of specimens may afford. The phenomenon of phanerocodonic and 

 adelocodonic gonophores being borne by one and the same species of hydroid rests upon no valid 

 evidence, though its occurrence has been maintained in more than one instance, and I am far 

 more inclined to regard the unsymmetrical, irregularly- lobed bodies of Alder's Corymorplia nana 

 in the light of misshapen monstrosities, occm'ring in an individual instance, than as a constant 

 and normal phenomenon ; and this view I am the more disposed to adopt as Alder's figures 

 convey no idea of true sporosacs. 



It is also a point for further investigation to determine whether the peculiar club-shaped 

 form attributed by Alder to the solitary marginal tentacle of the planoblast is not the result of a 

 contracted condition of this organ. Alder evidently thinks not. 



Halatractus nanus, Alder. 



CoRYMORPH.i NANA, — Alder, Catal. Zooph. of Northumberland, Durham, p. 80, pi. vii, figs. 

 7 and 8; Suppl. Catal., p. 9, pi. xi. Allman, in Ann. Nat. 

 Hist, for IMay, 1864.. Hincks, Brit. Hydr. Zooph., p. 130, 

 pi. xxii, fig. 3. 



TROPHOSOME. — Htdrocaultis about one half an inch in height, marked by 

 longitudinal opaque white bands, and tapering towards its proximal end, where it 

 terminates in a blunt point, which is surrounded by a loose sheath of filmy perisarc. 

 Htdranth with from fifteen to twenty tentacles in the proximal zone, and about 

 sixteen or eighteen in the distal, where they are disposed in two imperfect rows. 



GONOSOME. — GoxopiiORES forming a verticil close to the proximal zone of 

 tentacles ; medusa with the summit of the umbrella rounded. 



