270 
correctness of this assertion the author selects 8 species of the 
128 treated in his work, in which the characters taken from the 
margin and operculum either are not found in some species oi 
a certain genus as defined by him or in some species of two 
other genera show a supposed variation or inconstancy, and as a 
consequence hereof he prefers [to use as chief characters in the 
limitation of most genera diversities in the arrangement of the 
hydrothecae or in the form of the colony, but at the same time 
he lays the chief stress on the opercular apparatus and the form 
of the hydrotheca in the diagnosis of the two genera Diphasia and 
Abietinaria. I intend here to undertake a critical examination oi 
the genera proposed by Prof. Nu tting, and under each genus ] 
shall mention not only the species in which this author has thoughl 
he found inconstancy in the hydrothecal characters, but also those 
which to my opinion ought to be referred to another genus. — 
In his work on the American Sertulariidae Prof. Nu tting 
gives the following diagnosis of the genera as far as concerns 
the trophosomes, but as the gonosomes on the whole play a verj 
insignificant systematic part, I have not found it necessary to refei 
to that part of the diagnosis concerning these structures. I shal 
later mention these structures in my own diagnoses of the same 
genera. 
Sertularia (L.) Nutting. 
“Hydrotliecæ in strietly opposite or rarely subopposite pairs 
Stem and branches normally divided into rogular internodes, eacl 
of which bears a pair of hydrothecae, but sometimes there are raor< 
than one pair to the internode, in which case the hydrothecae an 
strietly opposite. Operculum normally of two flaps.” 
Thujaria (Flem.) Nutting. 
“Hvdrothecae normally subopposite to alternate, and more thai 
two to each internode. Internodes vary greatly in length. Hydro 
thecae with smooth margin, or with one or two teeth usually mon 
or less immersed in the hydrocaulus. Operculum of one abcaulim 
flap, or of two flaps.“ 
