124 THE VOYAGE OF H.M.S. CHALLENGER. 
which forms a wide, continuous structure separating the ridges. This latter form has also 
a finer and more delicate structure than Pachyseris speciosa. It may be distinguished as 
Pachyseris haimei, n. sp. j 
Locality.—Tahiti. 
Genus 4. Cylloseris, n. gen. 
Corallum compound, consisting of more or less irregular, semi-incrusting, thin, 
explanate expansions, the under surface of which is faintly granulated and marked by 
very delicate costal striations. The upper surface very uneven, owing to the development 
of subconical, elevated, compact, perpendicular projections, which form neither longitudinal 
crests nor continuous transverse ridges, but which are often arranged in a subconcentric 
manner ; these projections apparently formed by short, irregular, transverse flexures of 
the corallum at the margin, with consequent thickening and elongation by growth. The 
calicles are scattered and numerous, situated singly, both in the upper angle of the 
elevations, which consequently form large platforms below the calicles, and irregularly on 
the sides and extremities of the larger projections. The fossa extremely small. The 
parent calicle indistinguishable. The septo-costz take the form of extremely delicate, 
very granulated, entire striations over the whole surface, continuous from centre to centre, 
giving a very even appearance to the projections. Columella tuberculate or sub- 
styliform. 
The subconical or subcylindrical, elevated projections of the surface, with the almost 
inconspicuous cells and septa, give a peculiar appearance to this genus, and easily serve 
to separate it from all other Fungida. It has many points of alliance with the fossil 
genus Hydnophorabacia, This is clearly the undescribed genus referred to by Professor 
P. Martin Duncan in his Revision of the Families and Genera of Madreporaria, p. 164. 
Cylloseris incrustans, n. sp. (Pl. VI. figs. 4-40). 
Corallum incrusting, often free for a large extent, much bent and contorted, and 
extremely thin at the margin. Coste closely crowded, very faintly marked, almost 
obsolete ; the under surface uneven, and closely and irregularly undulate. The projections 
of the upper surface are from 2 to 7 mm. high, irregular, subconical, often with an elongated 
base, and bent, and often continuous with one another; acute or rounded, rather close, 
sometimes crowded. Calicles, very small and shallow, the fossa being from about 0°5 mm. 
to 0°75 mm. wide; they are situated singly both at the base of each of the projections, in 
the upper angle, and on the larger and thicker projections. Septa of three or four cycles, 
often much elongated, very thin, appearing as fine striations, and scarcely distinguishable 
with the naked eye; continuous over the projections from centre to centre, but on the 
