334 M. C. Mereschkowsky on the Hydroida. 
exists no Thecaphorous Hydroid in which the hydrothece are 
arranged in more than two rows; but even in the above two 
species the apparent arrangement in several rows is, funda- 
mentally, the result of the stem being composed of as many 
smaller stems amalgamated together as there are rows of 
hydrothece ; so that here the number of rows is only apparent. 
But in all the Hydroids in which the stems are not complex 
the hydrothece are arranged either in two rows, as in Sertu- 
laria, Thuiaria, &c., or im a single one, as in Plumularia, 
Aglaophenia, Hydrallmania, &e. In Polysertas, on the con- 
trary, although in all other respects it differs but little from 
Sertularia or Thuiaria, the arrangement of the hydrothece 
in several (6, 8, 10) longitudinal rows is a character that 
occurs without the stem being composite. This multiserial 
arrangement gives a perfectly peculiar aspect to all the species 
of Polyserias: the branches become thick, round, and longi- 
tudinally striated; the colonies are usnally large, and the 
branches long. It is characteristic of the whole genus, that 
on the principal stem the arrangement of the hydrothece is, as 
usual, biserial. 
The gonosomes are not very different from the gonophores of 
Sertularia or Thutaria, except that their arrangement may 
also be multiserial, like that of the hydrothece. 
When I gave a short description of the genus Polyserias in 
this journal some months ago*, I knew nothing in literature 
upon this type of Hydroids. Since the publication of my de- 
scription there has appeared the third part of the ‘ Proceedings 
of the Academy of Natural Sciences of Philadelphia,’ in which 
Mr. Clark, in a memoir upon the Hydroids of the Aleutian 
Islands, describes two species of Hydroids which undoubtedly 
must be placed in my genus Potyserias. Unfortunately the 
author has not paid sufficient attention to the significance of 
the multiserial arrangement of their hydrothece, and has 
ranged one of them in the genus Diphasia, and the other in 
Thuiaria. It is evident that this view must give place to 
mine, according to which all the forms should be united in a 
single genus, Polyserias. It was, moreover, only from this 
memoir that I learned that this polyserial form was de- 
scribed by Mr. Verrill, under the name of Diphasia mirabilis, 
as long ago as 1872, in the ‘ American Journal,’ and subse- 
quently in a Connecticut journal; and I do not think I am 
mistaken in identifying Diphasia mirabilis, Verrill, with my 
Polyserias Hincksivt. 
* Ann. & Mag. Nat. Hist., Sept. 1877. 
+ For the references to these citations see the synonymy of Polyserias 
mirabilis, 
