142 THE VOYAGE OF H.M.S. CHALLENGER. 
Genus 5. Lithactinia, Lesson. 
Iithactinia, Lesson, Mlustr. Zool. Paris, 1831. 
5 Milne-Edwards and Haime, Cor., iii. p. 28. 
53 Dunean, Rev. Madrep., p. 146. 
This genus is undoubtedly very closely related to Polyphyllia. Very few forms of 
the two genera are known on which to base comparisons, and of these it is certain that 
injury to the colony during the growth of many of them has considerably interfered with 
and obscured the true character of the form. Owing to the very porous and fissured 
structure of the basal wall, and to the thinness of the corallum in these specimens, which 
are all unattached, such injury with consequent malformation is very liable to occur. 
Two species are in the collection. 
1. Lithactinia pileiformis (Dana). 
Polyphyllia pileiformis, Dana, Zoophytes, p. 317, pl. xxi. fig. 4. 
Two specimens were obtained, They are dish-shaped or basin-shaped, with one side 
much drawn out, so as to give in the larger specimen a length of 15 cm. and a breadth of 
9 cm. Both specimens are peculiar in that they give the appearance of having been 
broken during life, while growth has continued around the edges of a rather large 
fractured piece, so that the added portion is continuous with the original part. This is 
borne out by the fact that the septa and coste in the lateral pieces are not in the same line 
with those of the more central portion and do not radiate from a common centre, but are 
directed more or less at right angles to them. .In both specimens also, and apparently 
confined to the original fractured piece, a very short, more or less subradiate, calicular 
trench is indicated, but not placed so as to be median to the whole corallum. The costze 
in this species are very distinct, denticulate and rough, irregularly confluent, and separated 
by narrow, elongated fissures. 
Locality.—Reefs, Fiji; brought alongside the ship by natives off Kandavu. 
2. Lithactinia galeriformis (Dana). 
Polyphyllia galeriformis, Dana, Zoophytes, p. 317, pl. xxi. fig. 3. 
Two specimens were obtained. One, the larger, is conically cap-shaped, drawn out 
laterally so as to give a length of nearly 13 cm. and a breadth of nearly 9 cm. The 
second is smaller and broadly saucer-shaped, but irregular. They both present the same 
appearance, due to fracture, as in the Lithactinia pileiformis; but there is in no part 
any indication of a subradiate calicular arrangement. 
The species is very close to the ‘preceding, but differs markedly in its much thinner 
