118 
THE VOYAGE OF H.M.S. CHALLENGER. 
circular mandible ; another much smaller, boat-shaped ; and a third of an oval form and 
of various dimensions. Dorsal surface granular, shining, vibicate, often with small circular 
deeply imbedded avicularia. 
Habitat. — Station 161, off Port Philip, 33 fathoms, sand. 
(?) Yar. japonica. 
Character. — Of much more delicate habit, the walls of the zooecia being thin, delicate, 
and transparent. The peristome very thin, and more constantly produced into a wide spout. 
Habitat . — Cobie, Japan, 8 to 50 fathoms. 
[North Japan, Captain St. John.] 
Notwithstanding a considerable difference in habit, as these two forms agree in many 
essential particulars, I have with some hesitation provisionally regarded them merely as 
varieties. The Japanese form is much more delicate in 
all respects, and the anterior avicularia, though of the 
same form as in the other and distributed in the same 
manner, are much smaller. The ooecia also appear much 
more numerous, and they present the peculiarity of 
remaining entirely open in front, apparently for a long 
time, as very few if any can be seen closed in. One 
character of the species which may facilitate its diagnosis is the great number of zooecia 
in the width of the trabeculae, and the frequently very regular way in which they are 
disposed in oblique, transverse rows. The operculum also in Retepora victoriensis is 
thick, and in var. japonica very delicate. 
(11) Retepora simplex, n. sp. (PL XXVIII. fig. 4). 
Character. — Zoarium about l //- 25 high, irregularly infundibuliform, rising from a 
broad base ; fenestra oval, usually with a projection on one side, about 
0 //- 025 x '015 and of about the same width as the trabeculae. Dorsal 
surface finely granular, no distinct vibices. Zooecia convex, broad 
and short, ovate, surface subrugose. Orifice orbicular, peristome thin, 
deficient posteriorly. Labial fissure nearly median, very short and 
terminating in a rather large pore. A minute labial avicularium with 
semicircular mandible (often absent) on one of the angles of the fissure. 
A few scattered prehensile avicularia (readily overlooked) on the front 
and a few elongated retentive ones behind or in the fenestrse. Ooecia 
lofty, with a trifoliate stigma (fig. 46), often widely open. 
Habitat. — Samboangan, 10 fathoms. Admiralty Islands. 
Fig. 28 . — Retepora 
simplex. 
Fig. 27 . — Retepora victoriensis var. japonica. 
