MADREPORA. 107 
what irregular. Axial corallites cylindrical, usually 1°8 to 2 mm, diameter, rarely 2°5 mm. ; 
15 mm. exsert; wall usually thin but firm, margin plane. Radial corallites round, open 
nariform to tubo-nariform or tubo-labellate ; the inner part of the wall not so prominent as 
the outer; others between are smaller or immersed; the prominent corallites are often 
arranged in irregular longitudinal rows; length 1 to 2 mm., diameter 1°5 to 2 mm. ; outer 
part of the wall firm but not thick, the inner part is delicate. Star not prominent, usually 
only the directive septa are recognizable. Corallum rather dense ; surface dense but reticulate 
in parts, strongly echinulate ; wall striato-echinulate. 
Pacific Ocean: Great-Barrier Reef area. 
a-c. Rocky Island. Saville-Kent Coll. 92. 6. 8. 269 to 271. T 
d. Green Island. Saville-Kent Coll. 92. 6. 8. 272. } Es 
e,f. Capricorn Islands. Saville-Kent Coll. 92. 6. 8. 273 & 161. (Var.) 
D. Branchlets on the under surface suberect and often of considerable importance. In other 
respects this Division resembles the M. spicifera group (C.a). 
101. Madrepora hyacinthus. 
Madrepora hyacinthus, Dana, Zoophytes, p. 444, pl. xxxii. fig. 2; M.-Edwards & Haime, Coralliaires, 
t. iii. p. 158; Rathbun, Proc. U.S. Nat. Mus. 1887, vol. x. p. 16; Bassett-Smith, Ann. Mag. 
N. H. 1890, vol. vi. p. 455 (mon Quelch, ‘ Challenger’ Reef Corals, p. 164). 
Madrepora vastula, Bassett-Smith (non Quelch), Ann. Mag. N. H. 1890, vol. vi. p. 455. 
Corallum vasiform, pedicellate, frond 2°5 to 3°2 cm. thick ; branches sparingly coalescent ; 
below, branchlets crowded and spreading, 8 to 12 mm. long, often proliferous; above, 
branchlets slender (about 3 mm. thick), nearly simple, sometimes proliferous, 12 to 18 mm. 
long. Corallites tubo-labellate, not fragile, 2 to 3 mm. long, lip not at all flattened ; cells 
open, with an indistinct star. Axial corallites cylindrical, prominent. The branchlets below 
are muricate (oblique), nearly like those above. The type specimen is a vase, 12°5 cm. in 
diameter. (Dana.) 
The specimens from the Tizard Bank, referred by Bassett-Smith to this species and to 
M. vastula, agree more nearly with Dana’s description than any other specimens which I have 
seen ; but the twigs on the under surface are not so long as might be expected from the 
diagnosis. They have the following characters :—Fronds 3°5 to 4 cm. thick, attachment 
lateral; rather regularly reticulate, composed of branches 4 to 6 mm. thick, with appressed 
tubular corallites and a few short spreading twigs not over 7 mm. long on the under surface. 
Branchlets on the upper surface arched ; two or more arise from a common base, and sometimes 
each is again subdivided. Axial corallites cylindrical, 2 mm. (rarely 2°5 mm.) diameter and 
1 to 2 mm. exsert. Radial corallites dimidiate or labellate, with a curved outer surface, and 
becoming shorter, nariform, and finally immersed on the main branches ; length 2:5 to 8 mm., 
diameter 15 mm.; wall firm. Very few truly immersed corallites occur in any part of the 
corallum. In the axial corallites the septa are in two cycles, but the second is very narrow ; 
