132 
MR. H. N'. MOSELEY ON THE 
Postscript, added February 22, 1877. 
I have, since the above was written, discovered that the group of stony corals known 
as the Stylasteridse is composed of true Hydroids, and have suggested that these should 
be grouped with the Milleporidse in a special suborder, to be termed Hydrocorallinse. 
(See Proc. B. Soc. no. 172, 1876, p. 99.) 
Description of Plates illustrating the Structure of Millepora. 
All the figures, with the single exception of fig. 5, Plate 2, represent the structures 
occurring in Millepora found at Tahiti, Society Islands, viz. Millepora nodosa. 
PLATE 2. 
Fig. 1. Ovoid thread-cell, confined in position to the bases of the zooids and general 
superficial layer, not occurring in the tentacles. 
a. The cell unexpanded. 
b. The cell with the thread fully projected. 
The respective lengths of the various parts of the thread and cell are drawn 
exactly according to measurements. 
Fig. 2. Three-barbed thread-cell, of the form peculiar to Hydrozoa, occurring in the 
tentacles of the zooids and also sparingly on the general surface of the coral. 
a. The cell with its head protruded and thread partially projected. 
b. The cell in the unexpanded condition. The figures are drawn exactly 
to measurements. 
Fig. 3. View of a portion of the corallum, magnified 2 diameters. 
Fig. 4. View of the surface of the corallum, magnified 80 diameters, showing one com 
plete system of pores, composed of a central calicle, which contained in the 
recent condition a mouthed zooid, and eight surrounding smaller calicles of 
mouthless zooids. 
Diameter of the central calicle =0-25 millim. 
Largest diameter of the whole group =1*5 „ 
Drawn by Mr. J. J. Wild, Artist to the ‘Challenger’ Expedition. 
Fig. 5. Enlarged view of a vertical section of the corallum. 
C. Zooid-cavity or calicle. 
B, B. Branches of the canal-system. 
Fig. 6. Section of the corallum cut parallel to its outer surface, showing a portion of a 
system of zooids. 
C. Calicle of mouthed zooid in horizontal section. 
C', C'. Calicles of mouthless zooids. 
