138 Scientific Proceedings, Royal Dublin Society. 
HEMITRYPA HIBERNICA, M‘Coy. 
Zoarium at times 13 cm. or more in height, irregularly conical 
or flabellate (Pl. vitt., fig. 5). Branches or columns fairly straight, 
generally 20 in 1 cm.; ribbed on reverse in young forms, slightly 
keeled on obverse, the keel being produced into pillars at intervals 
of about 0°5 mm. (Pl. vitt., figs. 2 and 3). These pillars may be 
0:25 mm. long, and, by expansions of their outer ends, form, 
parallel to each column, a slightly waved bar, which becomes an 
integral part of the tegmen (PI. vuit., fig. 1). 
Fenestrules elliptical, larger on the reverse; length about 
0°5 mm., width 0°25 to 0:3 mm. Typically 16 in 1 cm. measured 
along the columns. As few as 12 occur in one example. 
Dissepiments thinner than the columns. 
Zoecia typically 40 in 1 cm. measured, longitudinally (thus, as 
M‘Coy says, about three to the length of a fenestrule). 
Tegmen formed of “scale” (10, p. xxiii), distinctly continuous 
with the crests of the pillars that rise from the keels of the main 
columns, producing a delicate mesh with circular apertures, which 
sometimes appear by illusion hexagonal. ‘These apertures are 
alternately arranged in double series, each series corresponding 
with the series of zocecial pores beneathit. The bar formed by the 
crests of the pillars is so slightly wider than the scale, and than 
the midrib that results from their union, that the whole meshwork 
presents a very uniform texture (Pl. vitt., fig. 3). Its openings are 
wider in diameter on the inner face; from 32 to 46, typically 40, 
lie in 1 cm. measured longitudinally, and from 34 to 44 measured 
transversely. (‘I'he probable type-specimen shows variations from 
32 to 36 tegminal apertures longitudinally, and gives 40 on trans- 
verse measurement. Another specimen varies from 34 to 40 in a 
transverse direction). 
M‘Coy’s figure (2, pl. xxix, fig. 7, left-hand upper drawing) of 
an enlarged portion of the outer surface of the tegmen exactly 
represents what is seen in certain lights on the surface of the sup- 
posed type-specimen. But careful observation under a dissecting- 
microscope shows that this appearance varies with the direction in 
which the light falls. The dark mesh-structure can, in reality, be 
proved to be raised; it is the true tegmen. The white rings of 
