REPORT ON CORALS—DEEP-SEA MADREPORARIA. 205 
between the cost, and each divided into two by the septa which alternate with the 
costee. Septa, except the primaries, which are free, coalescing successively according to 
order, and forming deltoid figures, beset with a series of long outwardly-directed spines 
on their free margins ; attached beneath to the transverse trabeculs which separate from 
one another the perforations of the wall by a series of short processes, in the intervals 
between which their lower margin is free. Columella large, spinous. Animal provided 
with knob-bearing tentacles. 
I have founded this genus to contain two very remarkable corals, dredged in deep 
water, which are so fragile that it is astonishing that they arrived at the surface in such 
good preservation as that in which they were obtained. The two species differ markedly 
from one another, but have so many fundamental agreements that they must evidently 
be placed in the same genus. They are evidently closely related to the Stephanophyllias, 
but their corallum is so perforate as to be reduced to a mere lace-work. No corals 
immediately like them appear to have been procured before, or since, either in the 
recent or fossil condition. Specimens belonging to the genus were dredged on four 
occasions, all from deep water (over 1500 fathoms), and all in the Southern Hemisphere. 
Leptopenus discus, n. sp. (Pl. XIV. figs. 1-4; Pl. XVI. figs. 1-7). 
Corallum white, discoid, flat, excessively thin; its greatest height, which is in its 
centre measured to the top of the columella, being not more than 2 mm. Base con- 
sisting of a network composed of a series of long, delicate costal trabeculee radiating 
from its centre. These radiating trabecule bifurcate at regular intervals, and the 
number of them thus regularly increasing from the centre of the disc outwards, they 
terminate at the margin of the disc in a series of pointed spinous projections seventy-two 
in number.’ The notches between these marginal spines are not all equally deep, but 
those between every alternate pair are deeper. The less deep notches correspond with 
the major septa in position, The radial trabeculz are connected at regular intervals 
by a series of transverse narrow rounded bars of calcareous matter, which divide the 
spaces enclosed between the radial trabeculz into a series of transversely elongate, oval, 
or reniform apertures. These elongate apertures are transversed above in their centres 
by the under edges of the septa, and thus appear on the upper surface of the disc as pairs 
of perforations. There are about twenty-four or twenty-five apertures in each radial 
interspace between the centre of the disc and its margin. The wall of the disc is shghtly 
radially pleated, so that each of the costal trabeculae is made prominent beneath; whilst 
on the surface, the middle lines of the intervals between these trabeculz, corresponding 
with the lines of attachment of the septa, are thrown upwards to about the same extent. 
Near the margin of the disc, between the bases of the marginal spines, a small 
amount of excessively thin laminar matter representing true wall substance is developed 
' In the figure Plate XIV. figs. 1 and 2, seventy-one only are, by an error of the artist, indicated. 
