Limitation of Genera among the Hydroida. 363 
The genus Afractylis, as originally defined by Dr. T. Strethill 
Wright, was made to include all those forms of the older genus 
Eudendrium which are characterized by a fusiform shape of the 
polypite and a conical metastome, the greater number of the species 
moreover presenting a more or less complete retractility within the 
summit of the hydrocaulus, though nothing like a proper hydrotheca 
is ever developed. 
Among the forms, however, which Dr. Wright has included under 
his genus Afractylis are more than one generic type. One of these 
types had already been characterized under the name of Perigo- 
nimus by Sars, who described both the trophosome and the gono- 
some; while another had, under the name of Bougainvillia, been 
long ago described by Lesson, who, however, was only acquainted 
with the Medusa. That the Bougainvillia of Lesson is the Medusa 
of a Hydroid form of which the Hudendrium ramosum of Van Beneden 
(=Atractylis ramosa of Wright) may be taken as the type, has been 
shown by Dalyell, and confirmed by Wright and others. To this 
Hydroid and its allied species the name of Bougainvillia must ac- 
cordingly be restored ; and indeed we find Agassiz already arranging 
them partly under Lesson’s name, and partly under that of Mar- 
gelis, Steenstrup’s name for a Medusa which can scarcely be regarded 
as different from the Bougainvillia of Lesson. There thus remains 
only one form of Wright’s genus Atractylis which had not already 
received a distinguishing generic desiguation,—that, namely, which 
is represented by the Atractylis arenosa of Alder, whose gonosome 
has been recently so well described by Dr. Wright (Micr. Journ. 
n.s. vol. ii.). To this form, therefore, it will be necessary hence- 
forth to restrict the name Aéractylis. 
Atractylis arenosa, Alder. 
The following species cannot be regarded as otherwise than 
provisionally referred to the genus Afractylis. Two of them 
will probably turn out, when the gonophores shall have been 
observed, to belong really to the genus Perigonimus; while a 
third is undoubtedly the type of an entirely new genus. 
Atractylis coccinea, Wright. 
Atractylis miniata, Wright. 
Atractylis margarica, Hincks. 
The Atractylis margarica has been described by Mr. Hincks _ 
in the “Ann. and Mag. of Nat. Hist.’ for January 1863. It is cer- 
tainly not an Atractylis, but is the type of an entirely new genus. 
I refrain, however, from giving here a definite form and name to the 
genus which I know must be constituted for it, preferring to leave 
this duty in the hands of its discoverer, Mr. Hincks, who, I have 
little doubt, will take the same view in his forthcoming work on the 
Hydroida. 
3. Brmerta, Strethill Wright. 
Trophosome consisting of a branching rooted ccenosare ine 
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