486 J. W. Gregory & Jean B. Trench— 
Dacurarpia, Duncan, 1880. 
Dachiardia macgregori, u.sp. (Pl. XX, Figs. 2a, 6.) 
Diagnosis.—Corallum nodular; growth irregular; in places the 
surface is subplane and granular. The calices are widely isolated by 
compact exothecal tissue. Elsewhere the corallites project above the 
surface and are therefore free laterally ; and the formation of younger 
similar surfaces has left spaces filled with matrix in which the 
corallites are laterally free. Corallites circular, subcircular, and 
sub-hexagonal; often long and straight; fission exceptional. Septa 
two complete cycles which are long and join the columella, and 
occasional representatives of a third cycle. Endotheca scanty. 
Columella small but distinct. In some sections it appears even 
styliform. Pali indistinct, occurring as paliform lobes. 
Dimensions.—Diameter of corallum, about 50mm. ; diameter of corallites, 
2-4mm.; distance of calicinal centres, 5-7 mm. 
Figures.—Pl. XX, Fig. 2a, part of upper surface of corallum showing 
corallites and granular surface; x 3diam. Fig. 26, part of same specimen, 
showing transverse section of a corallite; x 2 diam. 
A finitves.—This interesting coral raises the question of the affinities 
of the genus Dachiardia which, when founded by Duncan in 1880, 
was placed next to Plesvastrea; he, however, remarked at the end of 
the diagnosis (p. 92), ‘‘Fissiparity occurs, but israre.” Subsequently 
in his Revision (1884, p. 101) he placed the genus amongst the 
fissiparent Astreans, in the alliance Luvordea. His figures of D. densa, 
the first of the two species which he included in the genus, show no 
clear evidence of growth by fission. The figure of his second species, 
D. lobata, gives clearer evidence of that mode of growth, and is 
therefore the most convenient type.of the genus; we select it since 
none has been previously nominated. 
D. lobata differs from D. macgregort by having twenty-four septa 
which are alternately large and small, so that the cycles do not retain — 
their hexameral symmetry. The calices in D. lobata are from 2 to 
21mm. in diameter, and are therefore only half the size of those in 
D. macgregort. D. densa differs by having smaller corallites and 
three cycles of septa, which, being relatively longer, appear far more 
crowded than in D. macgregort. D..densa also has more definite pali. 
Prestastrma, Ed. & H., 1848. 
Plesiastrea horizontalis, n.sp. (Pl. XX, Figs. 1a, b.) 
Diagnosis.—Corallum compact, nodular. Outer surface unknown. 
Corallites circular to subcircular; long, straight, and parallel. They 
are united by horizontal dissepimental exotheca which gives a 
tabulate aspect to vertical sections, but may not be visible in cross- 
section. Septa three complete cycles, all short; in those of the 
third cycle the cost are sometimes twice as long as the corresponding 
septa. Pali two crowns forming a regular well-defined circle around 
the small fascicular columella. The secondary pali are no larger 
than the primary. Endotheca scanty. 
Dimensions. —Diameter of corallites, 3mm.; distance of calicinal centres, 
5mm.; diameter of circle of pali, 1-5mm.; average vertical distance 
between horizontal exothecal dissepiments, 5 mm. 
