CARBONIFEROUS FENESTELLID®. DART) 
verse differ so materially in appearance that they might easily be 
mistaken for distinct species, were it not for their constant occurrence 
together in close proximity, and also that some of the fragments 
are so fractured as to show the gradual passage from the broad flat 
interstice of the obverse to the narrower and more convex stems of 
the reverse” *. 
What is here said to hold good respecting Polypora biarmica I 
find to be true, not only of the Fenestellide in particular, but of the 
reticulated forms of Polyzoa in general. Unfortunately for the 
cause of paleontology these facts have not been allowed to have 
their due weight in the description of the various species; and the 
result has been a needless multiplication of ill-defined and uncertain 
forms, very perplexing to the student and of doubtful benefit to the 
science. 
Bearing in mind the differences which I haye pointed out in the 
character of the individual polyzoon, it is no wonder that the early 
describers fell into this error when the determination was often 
made from fragments only, and these imperfect. 
More important even than this was that they failed to see the 
true character of the genus. M‘Coy believed that it would be found 
in Hemitrypat. Although some species of Henestella pointed in the 
true direction it was not discerned. At this time the character of 
the genus was a poriferous face, bare and smooth, the cell-pores 
level with the interstice and the latter having a faint keel. In 1874 
Messrs. Young and Young announced the discovery of a new 
Carboniferous polyzoont having the outline of a Fenestella, but 
with so many new features that they felt themselves justified in 
creating for it a new genus, Actinostoma, calling the species, to 
mark its specific character, fenestratum. 
In this species the true cell-pore stood well up above the inter- 
stice, a rounded nipple-shaped projection terminating in an opening 
or mouth furnished with eight denticles set around the margin. 
Below this was a smaller and more superficial opening, which may 
have been the base of some polyzoal appendage. On the prominent 
keel were elongated prominences with smaller ones at regular in- 
tervals: apparently they had been hollow, and may have been 
spines. This highly ornamental variety, presenting a strange con- 
trast to the majority of the Fenestellide, was really the more perfect 
form of Fenestella nodulosa, Phill. §, although not recognized as 
such at the time by the original discoverers. Still it is due to 
Messrs. Young to state that to them we are indebted for the first 
insight into the true type of the genus Menestella. Since then it 
has been ascertained that when Actinostoma fenestratum, Young, 
has been worn down by attrition or the action of water it becomes 
what we know as Fenestella nodulosa, Phill. It is a common 
occurrence for a frond to have upon it the characters of both Fene- 
* Quart. Journ. Geol. Soe. vol. xxxiy. p. 622. 
+ M'Coy’s Syn. Carb. Foss. Ireland, p. 200. 
+ Quart. Journ. Geol. Soc. vol. xxx. p. 681]. 
§ Geol, Yorks. pl. 1. figs. 51, 32, 33. 
Q.J. GS. No. 138. 7 
