CARBONIFEROUS FENESTELLID ©. 279 
various parts of the growth, which he describes as distinct species. 
Prof. M‘Coy subsequently, finding it only doubtfully described, 
gave a very full and accurate account of the polyzoon as usually 
seen. In Menestella irreqularis, Phillips partly describes the base ; 
Fenestella flustriformis, Phill., is the cast only of the reverse face ; 
Fenestella undulata, Phiil., has the cell-pores partly exposed, 
possibly by the removal of the outer cortical layer. In Fvnestella 
antiqua, M‘Coy, the specific distinction is the ‘inosculation” of 
the cell-pores. The specimen in the Woodwardian Museum is a 
weathered reverse from which all the substance of the polyzoon has 
been removed, leaving the base of the filled-up cell-pores exposed 
and apparently in junction. The distinction is founded upon the 
error of mistaking the reverse for the obverse face. The cell-pores 
are set obliquely in the interstice; the median keel causes them to 
spread out on the obyerse but not on the reverse face. 
The aged form of the polyzoon we have in the Ienestella carinata, 
M‘Coy*, in the Woodwardian Museum. The dissepiments at this 
stage are quite as thick as the znterstices, and the appearance on the 
reverse that of a Polypora. ‘The last stage is marked by an addi- 
tional thickening, more particularly of the dissepiment at its junction 
with the interstice, giving the hitherto straight interstice a series of 
sharp angular turns or zigzags. This, 1 have no doubt, is the 
Fenestella arctica, Saltert. Examples of both of these later con- 
ditions are found on Halkin Mountain, and frequently on the same 
frond. 
As yet I have referred only to the bare and denuded forms of 
Fenestella plebcia, M‘Coy. Quite recently I have met with what 
I have no doubt is a very near approach to the life-form of the 
species. There is no doubt about its true character, as in size, 
number, and distance of pore-cells it agrees in all respects with 
Fenestella plebera. As such I prefer to regard it rather than to make 
it into anew species. In it the cell-mouth is rayed as in Actinostoma 
fenestratum, Young f, and the number of denticles is the same. The 
pore-cell is rounded and projected well above the interstice. The keel 
is prominent, slightly waved, and studded at regular intervals with 
spiny processes of varying size. Between this, which is probably the 
nearly perfect form, and the bare one previously described we haye 
the several stages of the obliteration process represented by such 
forms as I’enestella formosa, M‘Coy §, and Menestella tubcrculo-carinata, 
R. Eth., jun.|| As Prof. M‘Coy was the first to describe this 
species, itis better that it should still be known as /vnestella plebeia, 
M‘Coy. By some authorities this species is regarded as identical 
with Fenesiella (Gorgonia) antiqua, Goldf.; and perhaps with good 
reason. For the present I prefer to confine my attention to the 
British varieties. 
* Syn. Carb. Foss. Ireland, pl. 28. f. 12, 
t Belcher’s Arctic Voy. 1855, vol. ii. p. 385, t. 36. f. 8, 
t Quart. Journ. Geol. Soc. vol. xxx. p. 681. 
§ Syn. Carb. Foss. Ireland, pl. 29. fig. 2. 
|| Mem, Geol. Sury. Scotland, sheet 23, p, 101, 
TZ 
