VINE : BRITISH PALAEOZOIC CTENOSTOMATOU3 POLYZOA. 81 
In Valkeria iwa the stem is repent and adnate, and what is more 
important, this repent stem is jointed at intervals, whilst in the fili- 
form stem of V. tremula the Zooecia are distributed upon it at certain 
intervals in groups. Between some of the foreign species of this 
genus and Ascodictya there appears to me to be a very close resem- 
blance in the whorl-like structures both of Zooecia and stem, but this 
will be referred to again further on. 
Family IX. Mimosellid^, p. 555. 
The Zooecia in this family are also contracted below, and are 
both movable and deciduous. The stem is erect in the beautiful 
M. gracilis, is confer void, and of a light brown colour. 
From this analysis it is very clear that it would be simply im- 
possible to adopt any of the generic names of recent species under 
which fossil forms could be placed. Indeed the peculiarly horny or 
membranous texture of the one, is only faintly apparent in the other; 
and so far as the fossil forms can be interpreted by their remains it 
would be very hazardous, and even reckless from the evidence avail- 
able, to say that any of the species had erect as well as creeping 
stolons or stems. The evidence of the deciduous character of the 
cells is likewise obscure ; yet it is impossible to interpret certain 
structural features of the fossil forms without supposing that the 
punctures or holes in some of my own examples of the Ascodicty- 
omidae as w T ell as in the Vinella repens of Ulrich were bases of 
deciduous cells. 
The structural features of one of the groups which I shall des- 
cribe presently may be referred to here. On plate IV. I give magnified 
illustrations, both drawn with camera lucida and to the same scale, of 
(1) Ascodictyon siluriense, Vine; and (2) of the recent Valkeria 
tuberosa, Heller, dredged at Naples, mounted and presented to me 
by Dr. Pergens, of Belgium. 
The Ascodictyon encrusted the outer portion of a very fine white 
shell, which, by careful manipulation, I have so reduced that when 
mounted in balsam, on glass, all the outlines of the cells, the ramifi- 
cations of the stolons, and even the dark "endosarcal" matter in the 
