PERMO-CARBONIFEROUS FENESTELLIDE. 197 
FENESTELLA CAVEA Sp. nov. (Pls. XV, XVI.) 
Description :—Branches thin, rather far apart, separated 
from each other by twice or three times their own width, 
branching somewhat frequently, giving the colony a slightly 
spreading habit. Cross-bars distinct, rod-like, much thinner 
than the branches, rather distant but at regular intervals. 
Fenestrules rectangular, about three times longer than 
they are broad. Non-celluliferous surface rounded, smooth. 
Celluliferous surface with a distinct carina, rising as a 
low wall with rounded summit, from a flat surface, which 
bears the cells. These are in two rows, their apertures 
are very small, circular, separated from each other by 3 
or 4 times their own diameter, occasionally so laterally 
placed as to indent the margin, and with exserted rims. 
There are regularly six cells in the length of each fenestrule, 
a character which seems very constant. 
Measurements:—In 10 mm. longitudinally 6 to 7 cross- 
bars. Length of fenestrules 1 to 1°5 mm., width °5 to ‘6 mm. 
Locality and Horizon:—Branxton (Upper Marine Series). 
Relation and differences:—The fine, widely separated 
branches and distant dissepiments give a characteristic 
appearance to this species. In most respects it resembles 
F. multiporata McCoy,* which has a similar habit, but 
it differs in having fewer cellsin the length of a fenestrule. 
This character seems a very constant one in the Fenestel- 
lide, as in every specimen yet examined, the number of 
cells never seem to vary more than one, and even this 
slight variation is generally corrected by allowing for 
the width of the cross-bar. 
In the form of the carina, F. cavea resembles F. fossula 
Lonsdale,” but differs in most other respects, including 
habit, size and shape of fenestrules, in its smaller cells, 
McCoy, (8) p. 208, pl. 28, fig. 9. 2 Lonsdale, (1) p. 83. 
