268 NATURAL HISTORY SOCIETY OF DUBLIN. 
present. Even when present, I should now, upon re-examination of 
the two Irish forms, quite coincide with Grenacher’s suggestion, that 
they represent but the discoid bases of certain of the spines, whose 
shafts may not have become developed. If they were truly linear or arcu- 
ate, or crescentiform spicula, as Carter represented, and as I had myself 
long thought, though always puzzled about it, they should naturally 
be apparent on the upper portion of an example when focussed by an 
observer, and yet I could not perceive them; they, in fact, only appear 
linear when seen edgeways at the periphery of a specimen. These ap- 
parently distinct spicula, that is, the bases of the spines, are, of course, 
really circular, and appear so when viewed at the near or upper portion 
of a specimen; but they are very pellucid, and hence hard to be made 
out, even with accurate focussing, and this seems to me to account for 
the puzzle that the assumed linear spicula could be seen only at and 
towards the periphery. 
So far, then, as I can see, the foregoing diagnosis lays down all that 
can be as yet absolutely stated as appertaining to the genus of which 
Carter’s A. turfacea is the type. Further accounts of its structure 
internally are given by Grenacher and by Greef in the papers already 
alluded to, but they are open to confirmation, and it may, therefore, 
be here useful, as briefly as I can, to presently try to convey their ob- 
servations. 
The form described by Grenacher, and called by him Acanthocystis 
viridis, is regarded by him as identical with Actenophrys viridis (Khr.), 
but as distinct from A. turfacea (Carter). Greef, on the other hand, 
considers the latter and Grenacher’s form to be identical, and truly 
none else but Actinophrys viridis (Kihr.). I would myself still venture 
to hold a different opinion, and regard it as not proven that Acantho- 
cystis turfacea (Carter) is actually the same as Actinophrys viridis 
(Ehr.). That form is figured by Ehrenberg as densely fringed by the 
pseudopodia, which are very short, say not more than one-third or one- 
half of the diameter of the body. Even assuming that the radial pro- 
cesses are really siliceous spines (the true pseudopodia overlooked), they 
are thus so far quite unlike either Grenacher’s or Greef’s or our Irish 
form in these respects; for in these the spicula are comparatively fine 
and long, the longer ones quite equal in length to the diameter of the 
body (if not, indeed, longer), not to speak of their occurring of two 
distinct lengths. In fact, Ehrenberg’s figure shows the radial processes 
only about equal in length to the shorter series of spines of A. turfacea. 
In the latter form, too, they are far less numerous and less crowded— 
could be without much difficulty counted—they do not form the dense 
fringe-like border shown by Ehrenberg. Hence it appears to me to be 
still a matter of doubt that Hhrenberg’s Actenophrys viridis is truly 
the same as Acanthocystis turfacea (Carter), or A. viridis (Grenacher), 
provided the two latter forms are distinct; until it should be proved 
that they are indeed truly identical, Carter’s name should for the 
present, at least, and unless A. wzdis (Ehr.) could be proved to be the 
same thing, maintain its currency. 
