8 Proceedings of the Royal Society of Victoria. 



the polypide, by means of which it can be withdrawn right 

 inside the zooecium, as in Fig. 11. Each of the long muscle 

 fibres (Fig. 12, on. f.) appears to consist of a single cell, and 

 at a point about the middle of each there is an oval 

 swelling ; here the fibre stains more deeply than elsewhere, 

 and this spot must doubtless be regarded as the position of 

 the nucleus (Fig. 1 2, n. m. /.) 



All that I have been able to observe concerning the 

 nervous system of Cryptozoon is the presence of an oval 

 ganglion, situated in the usual position between mouth and 

 anus. 



So far as I am aware, Cryptozoon is the only Polyzoon 

 which makes use of sand in the formation of its skeleton, 

 and it is interesting to find a Polyzoon acquiring a habit 

 with which we are already familiar in other groups, such for 

 example, as Foraminifera, Sponges, and Annelids. The 

 genus is obviously closely allied to Boiverhankia, as is shown 

 by the presence of the gizzard, and the aberrant stracture of 

 its ccenoecium may perhaps be best understood by comparison 

 with that genus. In Boiverhankia ijustidosa, for example, 

 the coenoecium is entirely chitinous. It branches dichotom- 

 ously, and at each angle of the ramification there is a close- 

 packed group of tubular zooecia. We have only to imagine 

 these zooecia to become more irregularly and diffusely 

 arranged and invested in a common sandy matrix, beyond 

 the surface of which the tentacles are protruded, and we 

 shall arrive at the condition of Cry])tozoon. Cryptozoon, 

 therefore, may be regarded as a Boicerbankia, which, for the 

 sake of additional protection, has acquired the habit of 

 agglomerating particles of sand on to the zooecia. 



It might perhaps even be doubted whether there exist 

 sufficient differences to separate Cryptozoon from Bower- 

 hankia, l)ut the fact that there are at least two totally 

 distinct species which form arenaceous nodes seems to me to 

 render desirable the erection of a new genus. 



I will now briefly enumerate the distinctive characters of 

 the two species. 



Cryptozoon wilsoni. 



The zoarium (Figs. 2, 8) forms dense, bushy masses 

 attached to foreign objects. Sometimes it appears to be 

 provided with a common basal agglomeration of sand 



