M. C. Mereschkowsky on a new Genus of Sponge. Ti 
It is with the purpose of adding some new facts which may 
serve to elucidate the nature of the creatures in question that 
I have set myself at once to describe my observations made at 
the White Sea upon a new organism very nearly allied to the 
Physemaria of Hiickel, and especially to Haliphysema echi- 
noides = Tisiphonia agariciformis, but which, at the same 
time, must undoubtedly be placed among the sponges. I 
shall therefore pass at once to the description of this inter- 
esting creature. 
In my first journey to the White Sea in 1876, I found in 
two localities*, upon the stems of Sertularie, a singular 
organism, which I met with again in 1877, in my last visit 
to this sea, so, fertile in unknown and often very remark- 
able animals. This time I found it seated upon a branch 
ot a Bryozoon, quite close to the islands of Solowetzky, at a 
depth of 2 fathoms. 
At first, considering its small size (the sponge measures 
only about 0°5 millim.), I thought I had to do with some Rhizo- 
pod, such as the graceful Clathrulina elegans of Cienkowski 
for example, and the more as the form of this sponge, which 
consists of a spherical head placed upon a long and thin pedun- 
cle, very much resembles that of the above-mentioned fresh- 
water organism. But closer acquaintance convinced me that 
the object in question was nothing but a very small sponge. 
The entire sponge is composed of two very distinct parts— 
namely, a very long and very fine peduncle, and a round ball 
placed at one extremity of the peduncle, the other end serving 
to attach it to Hydroids or to Bryozoa. The peduncle itself 
is composed of two parts, one of which is a very long and fine 
cylinder, sometimes a little enlarged at its upper extremity 
where the ball is attached (Pl. VI. fig. 1). The approximateT 
width of this cylinder is 0°02 millim. ; at its lower extremity it 
passes into the second part of the peduncle, which is nothing 
but a conical enlargement by means of the base of which the 
sponge is attached to foreign objects. This basal cone, as 
well as the cylinder, which is simply a prolongation of it, is 
composed of a very thin layer of organic material, probably 
consisting of syncytium, and of a great quantity of very small, 
rather stout spicules, which are placed horizontally in this 
organic layer, the whole forming together a fine although 
tolerably firm and elastic membrane, which serves as a wall 
* Once between the islands of Solowetzky and the town of Kem, 
at 35° 25' longitude, at a depth of 12 fathoms, on a stony bottom; a 
second time in the Bay of Onega, not far from Belogousicha, at a depth 
of 16 fathoms on stony ground. 
+ I shall give more exact measurements further on. 
