4 
The collection contains a single example only of this remark- 
able coral. Like its congener, it was dredged in Backstairs 
Passage at a depth of 22 fathoms. 
Genus PLATYTROCHUS, Milne Edwards and Haime. 
Platytrochus hastatus, Dennant. R.S.S.A., vol. xxvi., pp. 257-8. 
Pl. vi fig: 2. 
The recent coral can be exactly matched among the fossil 
representatives of the species from the Spring Creek, Muddy 
Creek, etc., tertiary beds. The fossils show a slight variation 
among themselves in the slope of the spear-like projection at the 
base, but the seven examples of the living form are more uniform 
in this respect. The latter were dredged in Backstairs Passage 
at 22 fathoms. 
Platytrochus compressus, Tenison Woods, sp. РІ. i., figs. 3a, b. 
Conocyathus compressus, Tenison Woods, Linn. Soc., N.S.W., vol. ii., 
pp. 302-3, pl. v., fig. 1. 
The examples, 22 in number, of this coral were dredged in St. 
Vincent Gulf, Backstairs Passage, and Investigator Straits at 
15 to 22 fathoms. Actual comparisons with Woods’ type from 
Port Stephens, N.S.W., show that they belong to his species, 
which must, however, be placed under Platytrochus, and not 
Conocyathus. "The supposed pali are the papilli of the columella, 
which, as in Platytrochws generally, invade the lateral boundaries 
of the fossa. The calice is more narrowly elliptical than Woods’ 
drawing indicates, and instead of the 48 septa shown, it really 
contains 54. 
The South Australian examples vary in size, probably accord- 
ing to age. Several correspond with the type in dimensions as 
well as in the number of septa, etc., but others, though larger, 
are proportionally narrower. I redescribe the species, and also 
figure a full-grown individual. 
The corallum is wedge-shaped and much compressed, especially 
inferiorly. Its sides and edges slope gradually to the base, which 
in most individuals terminates in a short stalk-like pedicel. 
There is no trace of adherence. 
The calice is shallow, very narrow, and not truly elliptical, as 
its long sides are straight or sometimes even bend a little inwards, 
but laterally, that is, at the ends of the major axis, it is regularly 
curved. The summits of the short axis are usually higher, and 
often much higher, than those of the long axis. In the calice 
figured, these axes are in the ratio of 100 to 42. 
The septa are exsert, finely granular on their sides, and vary 
in number from 52 in the smallest to 69 in the largest specimens. 
There are apparently four cycles and ten systems, of which the 
