cnt 
PROF. P. MARTIN DUNCAN ON MICRABACIA CORONULA. 565 
The costee unite in series before reaching the centre of the base, 
and carry one line of granules, and this appears to be the rule. 
On turning the corallum on its edge so as to see the junction of 
the septa and the coste, the interesting bifurcation is occasionally 
very visible and sometimes is marked by the thickening of the ends 
of the coste (fig. 3). Weathering or rubbing down, assists the 
demonstration. 
The columella is small and rudimentary. From these consi- 
derations the generic characters of Mcrabacia should be thus 
modified :— 
Corallum simple, lenticular, convex above, shghtly hollowed out 
below, resting on the edge of the basal disk. . Coste delicate, simply 
granular, bifurcating at the calicular margin. Intercostal spaces 
crossed by synapticula, and having a regular series of openings 
leading upwards into the interseptal loculi. Septa continuous with 
the intercostal spaces, and formed by the junction of a process 
from the two nearest coste, arched, denticulate, solid, unequal. 
Synapticula well developed in series, continuous or discontinuous, 
terminating moderately high up on the interseptal loculi, and ending 
below as intercostal bars haying canal-like spaces between them. 
Columella rudimentary. 
Remarks.—W ere the synapticula invariably continuous as pro- 
cesses from the base to high up in the interseptal loculi in Micrabacia, 
this genus would present but slight distinctions from Mungia, Dana. 
There are other distinctions, however, of greater or less importance, 
such as the regularity of the spaces on the intercostal grooves in 
Micrabacia and their irregularity in Fungia, the regularity of the 
synapticulate bars in the one and their irregularity in the other, 
where they are often confused by a kind of thecal growth at the 
base. 
In Fungia there is a curious overlap of large strata in relation 
to small ones, and the cost are echinulated; these characters are 
not seen in Micrabacia. ‘The young septa are often fenestrated in 
Fungia, but not in Micrabacia. 
The genus Halomitra has synapticula resembling those of Micra- 
bacia within the septal loculi, and the discontinuous synapticulum 
is a very Lophoserine character. 
Now Micrabacia is elder than Fungia, and the slight structural 
distinctions are therefore very suggestive of descent. 
Finally, there is now great doubt about the generic position of 
the species, Micrabacia Fitton?, I described in the Monograph of 
the British Fossil Corals, Paleontological Society, from the Gault *. 
The type has unfortunately been mislaid by its possessor, so it is 
necessary to consider the excellent delineations given on plate xiv. 
figs. 6-9, by De Wilde. 
One question is—Are the broad processes with blunt angular ter- 
minations costve from the apices of which thin septa appear to arise? 
If they are costz, the form is nota Micrabacia. The second inquiry 
* 2nd series, 1870, pt. ii. no. 2. 
