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THE VOYAGE OF H.M.S. CHALLENGER. 
left in decalcified specimens. The great difference between the wide reticulation of this 
variety and the densely convoluted and minutely fenestrate habit of the variety I have 
termed “ ccespitosa,” is very remarkable, if the two in reality belong to one species, 
which there seems little room to doubt. But it is to be remarked that an equally great 
diversity of habit exists in the arctic Retepora elongata or wallichiana, some specimens of 
which are distinctly fenestrate, whilst others are as distinctly reticulato-ramose, whilst in 
Hetepora imperati, which, as before observed, may be regarded perhaps merely as a variety 
of Hetepora elongata , the mode of growth is always truly fenestrate. I would further 
remark that there is a form which I should regard also as a variety of Retepora tessellata, 
and of which the only specimen I am acquainted with is in the Oxford Museum, in which 
the zoarium, besides being bilaminar, is exactly like an Eschara (but fissile) throughout, 
excejff in a few spots here and there, where it presents the true Reteporine character, whilst 
the opercula and mandibles are exactly those of Retepora tessellata and its varieties. 
This form, which seems to be as yet undescribed, might be termed Retepora eschar oides. 
§§ 2. Ocecium with a vertical fissure in front. 
(6) Retepora gigantea, n. sp. (PI. XXVI. fig. 7). 
Character . — Zoarium 2 to 3 inches wide, flabelliform, expanded, springing from a short 
thick stem. Fenestras rhomboidal or broadly ovate, about 0"T long, and very uniform ; 
trabeculae nearly cylindrical. Zocecia elongated, linear, quite 
immersed except the oral end, which forms a rounded pustulose 
elevation, in the centre of which is the sunken mouth. Anterior 
surface uneven, glistening ; dorsal coarsely granular, very irre- 
gularly areolated, and presenting a few scattered circular pits. 
Orifice immersed, circular, with a shallow sulcus in front, on one 
side of which is frequently placed a small avicularium with a 
semicircular mandible pointing obliquely upwards. In many, 
more especially of the marginal zooecia, the peristome rises into 
a blunt eminence or mucro. Ooecia deeply immersed, with a 
vertical fissure in front. Anterior avicularia (besides the 
oral) very rare, and of two kinds, one with an acute 
curved acuminate mandible pointing obliquely downwards and outwards (fig. 7, b.), and 
more rarely others of small size and oval form with a semicircular mandible (fig. 7, c.), 
and appearing like minute circular pits ; in fact they resemble the dorsal pits, which, 
however, never appear to be furnished with any mandible. Operculum semicircular, 
0"-006 x -0045. 
Habitat . — Station 148, lat. 46° 47' S., long. 51° 37' E., 210 to 500 fathoms, hard 
ground, gravel, shells. 
