REPORT ON CORALS — DEEP-SEA MADREPORAR1A. 205 



between the costae, and each divided into two by the septa which alternate with the 

 costae. 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 trabeculse 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 Steplianoph yllias, 

 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. 



Leptopenxis 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 trabeculse radiating 

 from its centre. These radiating trabeculse 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. 1 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 trabecules are connected at regular intervals 

 by a series of transverse narrow rounded bars of calcareous matter, which divide the 

 spaces enclosed between the radial trabecules 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 slightly 

 radially pleated, so that each of the costal trabeculse is made prominent beneath ; whilst 

 on the surface, the middle lines of the intervals between these trabeculse, 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 



1 In the figure Plate XIV. figs. 1 and 2, seventy-one only are, by an error of the artist, indicated. 



