BRYOZOA FROM FRANZ-JOSEF LAND. 67 
Myriozoum. 
Whether this genus should be retained is very questionable, 
but for the present it is more convenient to keep the name for 
M. coarctwm, Sars, and IL. subgracile. d@ Orb., remembering that 
in descriptive papers we may often have to use generic divisions 
which we are aware may ultimately be altered. 
The genus was created by Donati with I. truncatum, Pall., as 
the type, and it has been based to a large extent upon the 
zoarial shape of growth; and the definitions given by Donati, 
Sars (Leieschara), d’Orbigny, and Smitt would not justify its 
retention. The aperture of JZ. truncatum is nearly round, while 
those of IZ. coarctum and subgracile are schizoporellidan, with a 
well-marked sinus. 
There is, however, one character which may be of great 
elassificatory value, and that is the long tubes, which I have 
called pore-tubes, from the surface to the interior, and from one 
zoecium to another, causing the spongy structure of the zoarium. 
These tubes havea disk near the junction with the zocecium ; and 
in the middle of the axial tubes, which are often very long, there 
are similar disks (Pl. 9. fig. 6d; fig.7d). The shell-structure is 
terminated by a membrane (fig. 86) perforated by these pores ; 
but over this, as in the greater part of the Chilostumatous 
Bryozoa, there is another fairly thick and somewhat chitinous 
membrane (fig. 7 a) continuously covering the zoarium. The 
eell-contents of the tubes attach themselves to this by delicate 
threads (fig. 8); and thus by this connection there may be an 
interchange between the sea-water and the contents of the tubes, 
which again are in indirect communication with the contents of the 
zoecia. Although in other genera these tubes are not developed 
to the same length, the structure is very similar. 
In figures 6,7 (Pl. 9), drawn to explain these tubes, the way in 
which the diaphragm is folded when the polypide is retracted is 
also shown. This folding, which at first I called an opercular fold, 
occurs in a similar position in most of the Chilostomata, but the 
appearance of this diaphragm varies much in different species* 
and at different times. It is attached to the tentacular sheath, 
_ and is, as described by Nitsche *, a strong sphincter which can 
completely close the tentacular sheath-cavity. The central 
* Nitsche, “ Ueb. Anat. u. Entw. von Hustra membranacea,” Zeits. f. wiss. 
Zool. vol. xxi. p. 17. 
Sys 
