156 
G. W. Lee — Trepostomata. 
Stenopora haddingtonexsis sp. nov. 
Plate XV, figs. 3, 4. 
Description. —(a.) External characters. The zoarium is composed of cylindrical 
branches, solid in the examples that have so far come under notice, and averaging' 
2 mm. in diameter. 
The apertures are oval, and number some thirty-five along a distance of 1 cm. The 
junction-angles are usually occupied by the aperture of a cell much smaller than the 
average. The interspaces are fairly constant in thickness and bear a row of large 
close-set acanthopores, seemingly of one size only. Xo maculae or monticules have 
been observed. 
(b.) Internal structure. Longitudinal sections show that the zooecia are in their 
proximal portion parallel to the direction of growth of the colony, and after that 
bend gradually to the peripheral region, where, after a sharper change of direction, 
they are nearly at right angles to the surface. The increase in the thickness of the 
walls in the peripheral region is sudden and considerable. The thickening is practically 
uniform, there being only the faintest suggestion of moniliform structure. 
Tabuke are present in both the axial and peripheral regions, but are more specially 
abundant in the portion immediately preceding the peripheral region. 
The specimens examined are interesting in that they offer the rather unusual 
instance of acanthopores visible in longitudinal section. In the slide figured pi. xv, 
fig. 4, the plane of section is not absolutely median and a thin film of sclerenchyma 
consequently obscures the zooecial cavities. It is in this film that the acanthopores are 
shown as dark lines alternating with lighter ones. 
The ratio of axial region to diameter is approximately 0'5 : 1. 
Tangential sections show that the acanthopores, which on the surface appear to be 
of one size only, are really of two sizes and form a conspicuous feature. The zooecial 
tubes are oval in section. The junction-angles contain a small cell which is also oval 
in section, and is still visible in slides cut a considerable depth below the surface. 
More numerous slides than it has been possible to prepare would be required in order 
to ascertain the true nature of these small cells. Those that have been observed in 
longitudinal sections are tabulated, but the tabulation does not appear to be different 
from that of the zooecia proper. 
Distribution .—The specimens on which this species is founded are from the 
Sandersdean Limestone of Sandersdean, If miles S.S.E. of Haddington, near the top 
of the Calciferous Sandstone Series^ 
